As a computer tech, I generally advise people not to use Sleep Mode because Windows doesn't always come out of Sleep Mode properly, with everything working just like before going to sleep.

If you insist on using Sleep Mode, then quit Thunderbird first, and start it again when you wake up the computer.

Bruce, I hear what you are saying. But for years I haven't had this problem, and it only started occurring on one of my laptops. Both are Win7. I never use Hibernate because that is always problematic but putting the computer to sleep has never been an issue for me (shutting off screen, powering down hard drive only). My computers are on all the time so I don't manually put them in to sleep mode, but have set the power settings to dim the monitors, then shut off monitors after a period of time and then power down the hard drive after a longer period of inactivity.

Workaround is to just close and restart TB after waking up PC but I thought I'd check with forums for a solution since, as I said, this only started occurring recently, in last month or so