working from the theory everything is important (sometime it is not) simply reinstall Thunderbird from http://getthunderbird.com The issue is probably simply a misstated key in your registry, but a reinstall is far easier and less error prone that fiddling with the registry manually.

As data is separate from programs in Thunderbird that should get rid of the message and nothing else.

thanks Matt - odd thing is , I did shutdown/start-up a few times, made no diff, popup appeared, then on my current startup, all clean. I guess an install (possibly an update ?) if it becomes an issue should solve it

cheers

MJ

It depends on what that file does, or what calls it - at specific times. It may be idle for a while, until correct events cause something to call it - except it's missing, corrupted or a registry issue, as Matt said.

You might be able to re-register the dll. It may / may not help, but won't hurt. Fairly simple - just search "registering .dll".