I have done all this : remove avast, remove MSE, reboot, reinstall avast.
You also need to do each uninstall separately and reboot in between or there will be remnants (left overs) behind on your machine which may cause conflicts with other security software.
It sounds like you didn't uninstall both software correctly and that is why you are having problems now.
I recommend doing an uninstall of MSE first:
http://uninstallers.blogspot.com/ - 21b is MSE
Remember to
reboot after you uninstall MSE.
After this, do an uninstall and do a
clean install of Avast:
1. Save a copy of newest version of Avast (5.0.594) for the version you need and save it to your HDD:
Free –
http://files.avast.com/iavs5x/setup_av_free.exe 2. Download the Avast Uninstall Utility, aswClear5.exe
http://www.avast.com/uninstall-utility and save it to your HDD (it has uninstall tools for both 4.0 and 5.0).
3. Disconnect from the Internet at this time.
4. Boot into
Safe Mode (hit F8 repeatedly) and run the Avast Uninstall Tool.
5.
Reboot twice.
6. Install the newest version of Avast and
reboot twice.
7. Get Internet access and update Avast definitions.
8. Register your copy or add the license key for Free –
http://www.avast.com/registration-free-antivirus.php.
Let us know how this works for you. Thank you.