have you already tried to process the IDOC in foreground, e.g. in WE19?
or have you tried to re-process the failed IDOC?
It is extremely difficult to find the source of this error, for this one would need to know the whole IDOC with all its data, and how the vendor was before the IDOC got processed.
if it is a complete new creation, then it might be a little easier, because then you can mainly focus on the data in the IDOC, and how they are processed.
if the vendor already exist and you extend this vendor to new organizations then it is more difficult as you then potentially have a mix of creation and change.
one tipp: make sure that you have not 2 IDoc segments with the same data.e.g. several purchasing organisations and 2 of them are redundant.