Hi,
1. Verify whether the Anti Virus software is running on the machine of which you are taking backup. In case it is running, please disable it and then back up.
2. Verify the network traffic between the media server and the machine whose backup is taken. Also check the network card of the media server.
3. Also check the following technote's :
http://support.veritas.com/docs/249090
http://support.veritas.com/docs/241858
Hope this helps.