When I try to backup the C drive across the network, it only runs successfully for about 20 minutes and then suddenly starts filling memory, causing Windows to freeze for a few minutes until the backup finally fails.

I can backup the C drive to a local USB drive without errors.

This is Ghost 15 (15.0.1.36526) on Windows 7 Ultimate 64 bit with 6GB memory.

The event log shows the following, but I think it is just a symptom, with the core problem being full memory:

Error EC8F17B7: Cannot create recovery points for job: Drive Backup of OS (C:\).
 Error E7D1001F: Unable to write to file.
  Error EBAB03F1: Error performing inpage operation.
 Error E7D10046: Unable to set file size.
  Error EBAB03F1: The specified network name is no longer available. (UMI:V-281-3215-6071)

Details:
Source: Norton Ghost

There aren't any processes obviously using the memory when it is filling up, but if I use Process Explorer to pause VProSvc.exe, the memory stops filling.  Here's a screenshot after I paused it at 20 minutes, just before it got full enough to freeze Windows.  The "modified" memory is taking over:

This is Task Manger showing the state just after I paused VProSvc.exe:

Just for reference, this is how it looked at 12 minutes into the backup; pretty normal I think:

I would greatly appreciate any ideas.  Thanks.