hi Born To Be Wild,
Self-defense module protects avast! drivers from being modified by another agent or program. System Restore is one such. To protect itself, avast! self-dense monitors the current environment in real-time, and whenever a possible attack is detected, it will either notify the user that this is happening, or ask for a password, and will then ask the user whether the self-defense disabling action should be allowed?
This will occur whether avast! is password protected or not.
The problem with System Restore is that this action/option never occurs for the user, as System Restore initiates before reboot, and completes the restore on restart, and avast! will wake up to a new (older) environment than before, and will thus be disabled as a result. Not an expected outcome, but understandable under the circumstances.
Disabling self-defense ahead of time will prevent any/all issues with System Restore and avoid the need to repair/do a clean uninstall/install of avast! Just be sure to re-enable self-defense when restore is successfully completed.