Issue Summary
I found a reproducible issue in Microsoft Fabric Dataflow Gen2 when using SAP BW Application Server as the source and Lakehouse table as the destination.
The Dataflow Gen2 can refresh successfully if the Lakehouse destination was already configured. However, when I try to open the destination settings and rebind the query to an existing Lakehouse table, the destination wizard fails with the error:
Value should be defined
This happens during the destination selection / binding step, not during data preview or refresh.
Source Type
SAP BW Application Server through Power Query / Dataflow Gen2.
The query uses SAP BW cube functions such as:
SapBusinessWarehouse.Cubes Cube.Transform Cube.ApplyParameter Cube.AddAndExpandDimensionColumn Cube.AttributeMemberProperty Cube.AddMeasureColumn
Destination
Microsoft Fabric Lakehouse table.
The original load was created using the default Lakehouse destination and completed successfully. The Lakehouse table was created and refresh worked.
Later, I tried to change/rebind the destination manually to the same existing Lakehouse table and change the loading method from Replace to Append. At that point, the destination wizard failed with:
Value should be defined
Important Finding
I tested the same destination behavior with other sources:
Source Rebind to existing Lakehouse table
| SharePoint Excel | Works |
| Table from another Dataflow | Works |
| SAP BW source | Fails |
This suggests the problem is not caused by Lakehouse permission, workspace permission, table existence, or the destination wizard in general.
The issue appears to be specific to SAP BW source metadata / Cube.Transform schema validation during Dataflow Gen2 destination binding.
Reproduction Steps
Create a Dataflow Gen2 in Microsoft Fabric.
Use SAP BW Application Server as the source.
Build a query using SAP BW cube functions such as SapBusinessWarehouse.Cubes and Cube.Transform.
Configure a Lakehouse table as the destination.
Run the dataflow. The first refresh completes successfully.
Reopen the Dataflow Gen2.
Open the Data destination settings.
Select manual/custom destination.
Choose an existing Lakehouse table.
The wizard fails with:
Value should be defined
Expected Result
The destination wizard should allow selecting an existing Lakehouse table and saving the destination mapping.
It should support normal destination configuration such as Replace or Append, the same way it works for SharePoint Excel or another Dataflow table source.
Actual Result
The destination wizard fails before the mapping can be saved.
The dataflow itself can still refresh if the previous destination configuration already exists, but I cannot safely rebind or modify the destination settings.
Business Impact
This blocks production setup for SAP BW ingestion into Fabric Lakehouse.
We need to load SAP BW data incrementally into Lakehouse, but cannot reliably configure an existing Lakehouse table destination with Append mode using Dataflow Gen2 when the source is SAP BW.
Current Workaround
Use Dataflow Gen2 only to extract SAP BW data into a staging Lakehouse table with Replace mode.
Then use a Fabric Notebook or SQL process to load data into the final table, for example:
SAP BW ↓ Dataflow Gen2 ↓ Lakehouse staging table - Replace ↓ Notebook / SQL delete-insert or merge ↓ Final Lakehouse Delta table
This avoids relying on Dataflow Gen2 existing-table destination rebinding for SAP BW queries.
Request
Please investigate whether this is a known Dataflow Gen2 issue with SAP BW source queries and Lakehouse destination binding.
Specifically, please check whether Dataflow Gen2 has a bug or limitation when resolving schema metadata from SAP BW / Cube.Transform queries during existing Lakehouse table selection.
Error Details
Error message:
Value should be defined
Session ID from error dialog:
ee47c976-888c-408f-ab30-60d3245b00f6
Environment
Product: Microsoft Fabric
Feature: Dataflow Gen2
Source: SAP BW Application Server
Destination: Fabric Lakehouse table
Issue area: Data destination / existing Lakehouse table binding