I have a problem with generating .rdlc report. One of the columns has this expression:
IIF(CInt(Fields!MyColumn.Value) = 0 or Fields!MyColumn.Value is nothing,"Unknown",Fields!MyColumn.Value)
=IIF(IsNothing(Fields!MyColumn.Value) or Fields!MyColumn.Value is nothing,"Unknown",Fields!MyColumn.Value.ToString())
You could try validating without a comparison:
=IIf(Fields!YourColumn.Value , Fields!YourColumn.Value , "Unknown")
Or reversing your check (check if it exists, instead of checking if it doesn't exist):
=IIf(Fields!YourColumn.Value > 0 , Fields!YourColumn.Value , "Unknown")
Also, I'm not sure, but it may have something to do with using different value types in the same column. Try using the same value type for an entire column. For example, only output strings, or only output ints.
If nothing works you can also check for NULL values in your code and then set the value to 0 or -1 (or so). Then in your RDLC report you can check on that.