Hi Glenda,
When media server is sending data it patched it up in 512 bytes so after the backup is done it checks the validity of the data through diving the total data size backe up by 512, if it cannot be divided evenly then bptm thinks of it as an invalid data and hence a system error.
please do check up the following tech note, as per Veritas the condition applies mainly because of the NIC cards in use.
http://support.veritas.com/docs/262860
Chiao
Ankur Kumar