This has been observed to occur when a NetCommunity site visitor submits a donation form with a "Comments" field entry that exceeds 255 characters in length. 
The essence of the SQL driver error is that a string is too long for the corresponding attribute/container in the RE database, so the string truncates on the right while being inserted. Your specific case may contain an abnormally long string in a different field.

A transaction cannot be processed successfully in its current state. The transaction data can be manually entered into The Raiser's Edge, and then deleted from the NetCommunity plugin.

If you are bulk processing and do not know which transaction is prompting the error, you will need to do process of elimination to determine which transaction is the culprit.