Thanks for replying Richard - I appreciate the help!
I took what you said and did some investigative work. Prior to this previous run, my next journal entry number should have been 3479 so I did a search in the GL10000, GL20000 and GL30000 tables for this particular JE number and didn't see any (remember of course this is Fabrikam). For this particular map, I'm grouping by currency (our company uses Multicurrency) which there is only three and I have a GP Rolling Column setup for the Journal Entry number (which I found from eOne's knowledgebase). In following the kb article on their site, I assumed it would pull the next JE number from the GL setup in GP. So when I executed the map again, it took the next three journal entry numbers (next JE number is 3482) but then failed with the same message.
Any other thoughts on this?