SpySweeper did previously have false positive detection with ashDisp.exe, the avast icon and GUI interface so this may be the culprit in removing your icon, see if there is a way to restore this from SpySweeper, ensure your SpySweeper signature/detection file is updated as this FP should have been fixed some time ago.
If you can't resolve it download the latest version of avast and uninstall, reboot, install, reboot.