It isn't detected as an intrusion, just that it exceeds the maximum concurrent connections, so avast effectively can't get a look in.
Presumably this NNTP connection doesn't require SSL ?
Even so it would contribute to the concurrent total of connections, essentially this isn't an SSL thing but cumulative connections.
You can increase this Concurrent Connections maximum, this used to work in earlier versions of avast, I have modified the locations and ini file to reflect the latest version
- Concurrent Connections Error: You could modify the C:\Documents and Settings\All Users\Application Data\AVAST Software\Avast\EmailShield.ini (XP) or C:\ProgramData\AVAST Software\Avast\EmailShield.ini (Vista, Win7) file using notepad. Find the [EmailScanner] section and insert a new line after the section heading, and enter this MaxConnections=75 (if that line exists you can change the value to 75). Save the changes, the avast self-defence will ask if it is OK answer yes.
[EmailScanner]
MaxConnections=75
I believe the default concurrent connection limit may be as low as 20 (for mail & news together). This limit exists not to save resources, but to prevent connection looping in strange configurations, so the user can increase it without worry to, for instance, 75. The value 0 disables the limit.