Non-negative number required error while appending tables

NOTE:

I decompiled the assemblies that Power BI runs on and hooked up my debugger to drill down and find out whats going on and I was correct. The culprit is a bug in the Microsoft.MashupEngine.dll assembly, not something wrong with any data source. It will occur when the report is big enough.

Specifically:

The ReadPage and WritePage methods of the Microsoft.Mashup.EngineHost.Services.TransformingPagedStream class both use the following line (or equivalent because the decompiler may not be accurate as far as semantics)

this.inputStream.Seek((long) (page * this.inputPageSize), SeekOrigin.Begin);

'page' is a 32-bit integer here and so is 'this.inputPageSize'. So when the page number of the stream seek operation gets high enough, the page*this.inputPageSize multiplication operation eventually gets larger than the max 32-bit integer value of 2,147,483,647, which causes the operation to return a negative number due to the overflow.

That value is *then* converted to a long. What needs to happen is that the 'page' or 'this.inputPageSize' 32-bit integer needs to be a long in the first place so that the multiplication operation does not cause an overflow (or one of them needs to be cast at the time of the multiplication operation).

This negative number result is passed down through a few other functions until it hits the spot where we are seeing this exception in the stack-trace provided by the original poster.

Hope a dev can see this and patch it - seems like a pretty big bug.

Layman's terms:

This is a PBI Desktop bug, not a data source bug or something wrong with the way you built your report. The only thing you can really do until it gets patched is try and shrink your data source(s) so none of them hit this limitation.