Cannot convert field of type NUM to BYTE

System Details : 4.1 SP8

I have an issue only experienced in WEBI whereby I get an error message (attached) and it is stopping me from creating a report. If I test this issue in the IDT first by creating a query the object values are returned with no problems and no error message. I also tried testing this using Lumira which also runs successfully.

The universe is built over an ABAP query and uses the SAPJCO connector. I have attached screenshots of the setup. Does anyone have any clues about what's going wrong here? I have tried changing the data types in the IDT but still have no success. Having just spent the last 5 hours doing an SP upgrade from SP6 to SP8 I'm now running out of ideas and patience.