Hi RedFan, thank you for your report. I have just tried the latest AVG beta IS build with the eM mail client configured to gmail account and everything worked just fine. Could you please try it again and send us logs for further analysis?
Just install the AVG client, enable debug logging (Menu → Settings → General → Maintenance) and try to send/receive emails.
Once done, please go to the c:\ProgramData\AVG\Antivirus\log folder and send us all *.log files in the zip archive (you can upload them into the ftp://ftp.avast.com/incoming server with login anonymous/anonymous). Let me know if you need any assistance with it. Thank you!