The backup of a Windows 2003 file server is running to completion,
but about one day in three ends with a return code of 12.  The client
error log shows ANS4039E messages on the days it fails, with a return
code of -53.  That return code means an invalid host name was
specified in attempting to establish a TCP/IP connection.

--> This is a short extract from the error log. The ANS1809W messages
occur with good backups too.
11/05/2006 01:07:29 ANS1809W A session with the TSM server has been
disconnected. An attempt will be made to reestablish the connection.
11/05/2006 01:07:32 ANS4039E Could not establish a session with a TSM
server or client agent.  The TSM return code is -53.

--> This is from http://tsmwiki.com/tsmwiki/DsmcReturnCodes
#define DSM_RC_BAD_HOST_NAME       -53 /* TCP/IP invalid host name
specified */

The backup is being run across our campus network, not within the
machine room, but we have verified that all links between the TSM
server and the client are gigabit, not 100 megabit.

The fileserver is holds about a terabyte. The client is at version
5.3.3.0.  The TSM server is at 5.3.0.2.

I don't understand how the error occurs on some days, but not others.
The server name in the dsm.opt file is not being changed on random
days. Could a failing network card on the file server cause this?
Any other probable causes?

Thank you,
Keith Arbogast
Indiana University