Site using apps Engine with the 'write to SQL DB' function produces this error intermittently.
Tried to replicate it a few times, on different PCs, but all seemed to be writing to the SQL DB and the local Excel register.
I googled, and while there were some suggestions that the error might be caused by empty fields (null values) being passed - I didn't want to muck around with the code unless I could replicate the error.
I then found a post that suggested the error could be caused by the length of string being written to the DB.
Ran another proposal with a long title (over 50 characters) - got the error. Yay.
I checked with the DB guy and all string fields were set to a maximum of 50 characters. The proposal title field on this occasion was over 50 - so we changed all 'Document Informtion' fields to MAX in the DB.
Tested - no error.