File system restore hangs for a very long period on "requesting previous index" before job finall (4042378)

A file system restore of files on a remote client machine (of many files or a single file) hangs with "requesting previous index" almost immediately after the job is launched.

The job does not fail but after several hours continues to write and the restore completes many hours later.
The line the restore hangs on is:

Job Message 2011/06/08 16:17:58 85 Data Plugin WEBTEST Requesting backup index

The restore may be from a backup of a large number of individual files in the in the original backup and this will cause the index transfer from the Netvault server to the temp directory of the Netvault client to take longer.
In this case however restores of individual files were being successfully carried out from backups of equally large numbers of files on other client machines.