Do you use Outlook or Outlook Express (or similar type of email program)? In other words, do you use Internet Mail Provider or Outlook/Exchange? If you disable “insert notes into message” is the problem out? If you use Outlook program you can try insert into avast4.ini file into [MailScanner] section following line:
UseAlternateRtfSyncing=1

(if [MailScanner] section doesn’t exist, create it - so insert to the end of ini file following text):
[MailScanner]
UseAlternateRtfSyncing=1