Every time that EF Worksheet gives me that mystery error its the 1116 attachment, I dont know why it cant have a better explanation somewhere. 

Made me crazy the first time it happened, it was a return with a 1310 and it kept making me think it had something to do with the 1310 and something needed to be attached for it.   I think it might show up in a diagnostic somewhere, but by the time you go looking for that youre so pissed off you probably skip right over it.