Provide the exception which raised the dump, I will suppose something like SYSTEM_ON_COMMIT_INTERRUPTED?
Perform a fast and easy where-used search on this exit and you should notice that it is executed during the save proces (in CO_BT_ORDER_POST) so not a PAI exit (many of those carry either an exception or a returned parameter for error) this one is not suitable for error message (too late)
Did you look for other exit/BAdI/Enhancement available in package CO for your transaction?
