Didn't know that vendors belong to SD .
Did you check your data, what length has the SWIFT code in your IDOC?
The CREMAS Idoc creates bank master data too if the bank is not present in the system.
SWIFT code is a field in the bank data. Check it in FI03 transaction
It further depends on the customizing of country specific checks whether SAP is checking the SWIFT code (active box for Bank data in section of further checks)