Hi All,
Thank you all for your help.
I eventually found what I was looking for. In transaction SM21 the error message is sitting there. Therefore it seems when the IDOC is sent all looks good on the sender side, but because there was a missing segment in the IDOC it was not received, however the error clearly shows in SM21 on the receiving system i.e it has the name of the missing segment and everything.
Thank you all once again for your help, it was much appreciated.
Wish you all a nice week further. 