Partition backup results in 0 bytes tib file

I'm having a problem using True Image 2010 to backup a Windows 7 partition.

I'm backing-up to an external drive on a network. All seems to go well until I check the tib file that has been created. I then get an error telling me that there's a problem with the file. On closer inspection I see that the file created has 0 bytes.

I have backed-up other files (documents, settings, emails etc) to the same drive without any problems at all. It's only copying the whole partition that throws up the error.

Any ideas anyone?

Thanks
David