This is known bug BG 2421304.  The Post Gift Batches procedure will end in error when trying to create the classification indicated by an attached benefit when the name_id on the batch item is greater than nine.

The workaround
is to manually create the classification indicated by the benefit for the individual in question under the account.  Once done, posting will complete as the procedure will detect the existence of the classification and by bypass the code containing the bug.

If you receive the error noted above and the workaround does not resolve the issue, please create a support request at providing the details of the issue and referencing this solution.