I, too, experience the "127.0.0.1 not responding" message today after Avast updated itself. (Win2K, Thunderbird 0.9). After a while I finally gave up trying to the the two mail providers to start in Avast, and told TB to directly access the POP servers. Which works fine. Reading this thread I am told that Avast no longer needs the 127.0.0.1 re-direction, and scans mail transparently.
I am not sure it is actually doing so -- I am used to seeing a notification in my e-mail message headers that Avast has found the mail to be clean.
None of the e-mails that I've received today have such a notation in the mail headers . . . . what's a good test to confirm that Avast is scanning my mails?
PS. An earlier post suggests adding "IgnoreLocalhost=0" to the [MailScanner] section of my avast4.ini file, but there is no [MailScanner] section in my avast4.ini file