Messages for input and outbound processing

[Eggy]

Questions about this idoc status message can be found all over the place. You process an idoc, it gets status 51 and the very helpful status message is "Messages for input and outbound processing". No idea what went wrong or how to fix it.

A very common answer is to use BD87 to see where the message is coming from. Unfortunately there is no additional information whatsoever to be found there. Just the same message.

Another suggestion is that there may be messages in the Application Log, trx SLG1. I've checked all kinds of logging there, but nothing relates to the idoc message.

It's clear that SAP is convinced there are messages... but apparently doesn't want to tell me what they are. Most 'solutions' I've been able to find is people giving up and using different methods or idoc types. That can't really be the answer... can it?