Depending on the frequency of your backups with acronis, you could disable System Restore altogether. Are you saving the backups in a separate partition (a different physical disk would be better, if possible)?
About avast, I would recommend downloading the latest stable version (of the same edition Free/Pro/AIS you are currently using) again. Then run the installation (as administrator if possible). Once the installation finishes, please reboot.
The re-installation (just over the current one) probably will solve most problems with your previous program update.