I have just downloaded and installed the 1065 build of FB to get around an issue and when I run it I am presented with the dialog for entering a license key. It also says "Invalid license key: The license key is only valid for builds dated : 18/09/2010 or earlier. To use this build you must renew your subscription."
In fact, .642 is the newest one that I can run, despite my software assurance being valid until 18th Sept 2011. 
Hi Mark
When you renew your subscription, you need to download and install your license key again as it will be regenerated with the new subscription date.
Vincent,
As you can see in my original post, I already did that. I noticed however, that the file hadn’t been updated on your servers and still had a 2010 expiry.
One of the support guys has regenerated it for me and it is now working.
Mark