- Is the System Virtual Memory settings for paging file is set to Automatic.

- what is the version of BE.

- OS version.

If the settings is not set to automatic, then set it to and restart the server.

please post some more details...

Regards.

• you may try moving it to another drive 
• Have the initial size be at least 1.5 times bigger than the amount of physical RAM. Do NOT make the Pagefile smaller than the amount of physical RAM you’ve got installed on your system.
•  Make its initial size as big as the maximum size. Although this will cause the Pagefile to occupy more HD space, we do not want it to start off small, then having to constantly grow on the HD. Writing large files (and the Pagefile is indeed large) to the HD will cause a lot of disk activity that will cause performance degradation. Also, since the Pagefile only grows in increments, you will probably cause Pagefile fragmentation, adding more overhead to the already stressed HD.
• Do not place multiple paging files on different partitions on the same physical disk drive.
• If you have a RAID-0 (Stripe Set) array, use it to store the Pagefile.
• Avoid putting a paging file on a fault-tolerant drive, such as a mirrored volume (RAID-1) or a RAID-5 volume. Paging files do not need fault-tolerance, and some fault-tolerant systems suffer from slow data writes because they write data to multiple locations.

Just out of curiosity, how big is the pagefile on that drive?

It is not necessarily that th pagefile expanded during your tape backup.  It is more likely that it expanded during a memory intensive operation like running dedup.  The pagefile does not shrink back once it is expanded.  You can re-create it using the procedure below

http://support.microsoft.com/kb/314834

Note that a re-boot is required to re-create the pagefile.

If your machine has insufficient RAM, the pagefile will again expand when it is short of RAM.  If you find that you persistently have a big pagefile, you should add more RAM to the machine, if possible.  Otherwise, you would be facing a page thrashing situation which will slow down your machine.