OK, the crash report indeed helped identifying a bug in the NNTP handler.
Could you please try an updated version? It should fix the problem.
Please follow these steps:
1. Stop the Internet Mail provider
2. download
http://cat.asw.cz/misc/ashmaisv.zip and extract its contents to the avast folder (overwrite ashMaiSv.exe - it shouldn't be locked thanks to 1.)
3.start the Internet Mail provider
Please let me know if there're any problems...
Thanks

Vlk