Here's a snippet from the EmailCRX log.... where thunderbird 2rc1 fails to log in.

Local POP server 0 idle
Listening...
server 1 reset
6 bytes available
cr/lf found at offset 5
rec'd -CAPA
CAPA
+OK Capability list follows... TOP USER UIDL
12 bytes available
cr/lf found at offset 11
rec'd -AUTH LOGIN
AUTH
+OK Supported authentication mechanisms: LOGIN
10 bytes available
cr/lf found at offset 9
rec'd -dHJhY3k=
Unhandled - dHJhY3k=
100, 72, 74, 104, 89, 51, 107, 61,
Disconnected...
POP reader idle

comments? suggestions? (my other clients log in just fine...)

The sequence should be :
USER yourusername
then :
PASS yourpassword

Do you have SSL selected?

SSL, not AFAIK....

Whatever it was, I've got to drop it. The issue knocked me off the air: changed my password with my ISP, and generally screwed things up royally. I don't need T-bird anyway... and yesterday's hassles are not worth experimenting with again today.

I think it's TB, not you, btw...