Forum Discussion
Power BI error: file 'xldc.cpp', line 3938, function 'XLAggImpl_Set<1,1>::Accumulate'
Hello all,
I'm experiencing this error on report created in Poer BI Desktop (Cloud, Version Nov 2025) ever since approx. 12. Feb 2025.
The strange thing is that the report is published and updated daily since months. The done changes on 12. Feb are minor, no major changes in the data model. Still, I constantly keep receiveing this error, but sadly there are not hint, which part in the data model is causing this error.
I also tried to upload a much older version of the report which was published and updated successfully months ago. But if I try now, it also causes the same error.
Any ideas on how to troubleshoot this?
Thanks!
BR,
Stefan
HI StefanGr,
Thank you for the update, your latest test provides valuable insight. Since the error still appears after removing all visuals and report pages, it suggests the issue is not with visuals or measures, but rather with the data model processing, such as data loading, calculated columns, or transformations. This supports your idea that the fact table may be the root cause.
It would be helpful to focus on the fact table, particularly the calculated columns. Try creating a copy of the PBIX file, remove all calculated columns from the fact table, and refresh. If the error disappears, reintroduce the columns one at a time to identify which one causes the issue. This step-by-step method can help isolate the problem.
Also, check the data quality and data types in the fact table. Mixed data types, unexpected nulls, or incorrect type conversions can cause internal aggregation errors. Setting data types explicitly in Power Query may help prevent this.
You could also test the fact table separately by loading it into a new blank PBIX file. Start with a few columns and add more gradually to see if a specific column or transformation triggers the error. Reviewing and disabling recent or complex Power Query steps may also help pinpoint the issue.
Lastly, since older versions of the report are failing too, the problem might be related to a recent engine or version change. Testing in the latest or a previous stable version of Power BI Desktop could help determine if the environment is a factor.
Thank you.
10 Replies
Hi StefanGr
I ran into the same error recently on a report that had been refreshing fine for a long time. In my case it wasn’t the whole model, it was one “bad” visual/measure that was crashing the engine.
From my experience what troubleshooting steps i took was:- Open the PBIX in Desktop.
- Go through the pages one by one and temporarily delete or hide visuals (on a copy version)
- As soon as the error stops appearing, you know the last visual you removed is the one causing it.
- Check the measures used in that visual and try to simplify them (remove very complex filters, DISTINCTCOUNT over huge tables, nested IFs, etc.) Then tested again.
A couple more things that helped:
- Reduce data for testing: filter the report to a smaller date range or one customer and see if it still fails. If it only crashes on “all data”, you might need to aggregate the data more or create a summary table.
- Try another Desktop version: install the latest Power BI Desktop and open the same PBIX there. Sometimes these internal C++ errors are version‑specific and disappear after an update.
It’s a bit of trial‑and‑error, but in my case once I rewrote the problematic measure and reduced the rows that visual was hitting, the error went away both in Desktop and in the service.
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Hi StefanGr,
The error file 'xldc.cpp', line 3938, function 'XLAggImpl_Set<1,1>::Accumulate' is an internal VertiPaq engine aggregation error in Power BI. Since the issue began around February 12 and older report versions that previously worked are now failing, this indicates the problem is likely due to an environmental, engine, or data source change, rather than minor model changes. These errors often result from backend engine updates, changes in data source schema (like data type changes, new nulls in numeric columns, duplicate keys, or increased data volume), or memory issues during refresh. High-cardinality columns or complex aggregation logic, such as DISTINCTCOUNT or iterator functions, might also contribute, even if those measures were already present.
For troubleshooting, check when the error occurs during refresh, opening the file, interacting with visuals, or publishing. If it happens during refresh, try clearing the cache (File -- Options -- Data Load -- Clear cache), disabling parallel loading, and turning off Auto date/time temporarily. You can also test by creating a new blank PBIX file, connecting to the same source, and importing tables one by one to identify any problematic tables or transformations. Finally, make sure you are using the latest stable version of Power BI Desktop or try a previous stable version if the November 2025 release might have caused the issue.
Thank you.
Hi StefanGr,
I wanted to follow up on our previous suggestions regarding the issue. We would love to hear back from you to ensure we can assist you further.
Thank you.
Hello v-sgandrathi : Thanks for the suggestions. Unfortunately, so far I have not found the error. I was slicing up my report an eliminated visuals, complex measures and also whole report pages. No change. My impression is, that the fact sheet by itself is the problem. The fact sheet has about 50.000 rows and approx. 30 colums, including several calculated colums. I did not try to dismantle the fact sheet so far, as this is the core or my report and the reason for using BI. I need to invest some more time to check what could be done in a different way.
Best regards, StefanHello v-sgandrathi : Thanks for following up. I was busy with other tasks and not time to troubleshoot the report.
Today I tried the ultimate strip down. I removed all report pages execpt for one and I removed all visuals from that page so that just some text fields and graphical elements remain on the page. Means there is no more measure or fact table used by this report page.
However, uploading this report to my cloud space, and trying to update this, the error persists.
I assume that updating the report also works through all steps to create the data model (importing tables, creating calculated columns in the model etc.). I can now try to remove calculated columns one by one to see which one is causing an issue, as I can be sure it's not coming from any of the visuals.
Or are there any other ideas?
Thanks!
BR, StefanHI StefanGr,
Thank you for the update, your latest test provides valuable insight. Since the error still appears after removing all visuals and report pages, it suggests the issue is not with visuals or measures, but rather with the data model processing, such as data loading, calculated columns, or transformations. This supports your idea that the fact table may be the root cause.
It would be helpful to focus on the fact table, particularly the calculated columns. Try creating a copy of the PBIX file, remove all calculated columns from the fact table, and refresh. If the error disappears, reintroduce the columns one at a time to identify which one causes the issue. This step-by-step method can help isolate the problem.
Also, check the data quality and data types in the fact table. Mixed data types, unexpected nulls, or incorrect type conversions can cause internal aggregation errors. Setting data types explicitly in Power Query may help prevent this.
You could also test the fact table separately by loading it into a new blank PBIX file. Start with a few columns and add more gradually to see if a specific column or transformation triggers the error. Reviewing and disabling recent or complex Power Query steps may also help pinpoint the issue.
Lastly, since older versions of the report are failing too, the problem might be related to a recent engine or version change. Testing in the latest or a previous stable version of Power BI Desktop could help determine if the environment is a factor.
Thank you.
Hi StefanGr,
Thanks for the update and for sharing more details.
Thank you for the detailed troubleshooting steps shared by both the Super User and CST member. Since the issue persists even after removing visuals, measures, and report pages, and older PBIX versions also fail now, it suggests the problem may not be related to the report logic itself but possibly to the VertiPaq engine environment or model metadata.
In such cases, it may help to recreate the model in a new PBIX by importing the base tables again and gradually rebuilding the model. This can help rule out potential model corruption. Additionally, testing the same report in a newer or older Power BI Desktop version could help determine whether the issue is related to a specific engine update.
Thank you and continue using Microsoft Fabric Community Forum.
Hi StefanGr,
we haven't heard back from you regarding our last response and wanted to check if your issue has been resolved.
Should you have any further questions, feel free to reach out.
Thank you for being a part of the Microsoft Fabric Community Forum!
