This happens an account has two or more soft credit relationships to prompt for. BAR tries to write a message to the comments field on batch detail when there is a soft credit relationship to prompt for. However if there is more than one such relationships then the comments become too long to fit in the comments field which is 256 characters.

You can avoid this by changing one of the soft credit relationships to not prompt anymore, or inactivate the classification on the account in question to exclude it from BAR and enter it manually instead.