Does Basis team applied any note or patch and after that you have been started getting this error?
If yes then need to investigate what note or patch applied and its impact.
You can test below 2 scenarios.
1. Create Test Z datasource in source system & then replicate it the BW system & then try infopackage creation & execution. If this is successful then some changes been happened in the source and/ or target system either by note/patch application or by manual error.
If this is the case because of patch or note implementation then you need to contact SAP support through OSS, they may provide any note or code changes or table entries to get rid of this error.
If not then go for below option:
2. Replicate datasource again & create new IP & execute it.
Hope this goes successful.
Thanks & Regards,
Pradip