Hi Arthur,
did you find a solution to this problem?
I am currently facing a similar issue - although instead of vendors I am trying to load customers.
I am using message type DEBMAS02 and for now I am only trying to create a single customer.
The customer is created and everything seems ok when looking at XD03 but the IDoc gets status 51 and no message - which means no indication of why the IDoc failed...
/Michael