problem udating portable firefox and thunderbird

I ran the automated updates for both Firefox and Thunderbird to upgrade to version 6. After restarting it goes through the 'applying updates' window, but then I get the following message:

"The update could not be installed. Please make sure there are no other copies of Firefox running on your computer, and then restart Firefox to try again."

After which FF/TB 5 are started normally. This now happens every time I try to start either program, causing considerable delay. I have tried both rebooting the machine and disabling add-ons, but the same error occurs.

I am running both programs from a CISP share mapped to the P:/ drive on my work computer. this is essentially the personal data drive provided on the company (university) server. I have updated this configuration before (3->4->5) with no problems