Power BI error: file 'xldc.cpp', line 3938, function 'XLAggImpl_Set<1,1>::Accumulate'

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.