Fixed

My virus checker is AVG, my secret decoder ring is PGP. PGP 9.0 uses the same Email intercept method as AVG, so they weren't compatible. Until...
AVG popped up to tell me that it's Email checking component wasn't running. Yes, I knew, I'd turned it off. So why was it telling me? Because the daily AVG update had updated it?

I turned it on, and sent myself an encrypted message. It worked...
and then I made the mistake of playing around with settings. It stopped working and refused to display its activate button.

So I upgraded to AVG 7.5 and it's working again on default settings, so I'm leaving it alone this time. AVG 7.5 setup has a repair option, so hopefully I can use that if it stops.

Now my only minor problem is that Thunderbird won't download Email when it starts up, only by request. A PGP glitch? Some dumb ISP setting as my Email box often locks up?