Can you close Incredimail and run the Mail Protection Wizard (Start Menu > All programs > avast antivirus > Mail Protection Wizard), choose the second option (non Outlook/Exchange provider) and then automatic protect all your accounts even the ones created in the future?
If that does not work, you can change manually the SMTP authentication options for something like this:
user_name#smtp_server_address
Fill your password and ask for saving it.
Hope this help.