No, I changed my system date.
As written before, there is an antipiracy feature to avoid using the trial time more than 60 days, what is much more than enough to evaluate the program. Very few (none) companies give such a trial period.
The program would not open. It just asked for a license key. But regardless I said if it were to happen.
What do you mean?
Did you buy avast and the key get corrupted because of the system time was rolled back?
When did you roll back? Before or after installing avast?
If you uninstall avast (Control Panel), use Avast uninstall feature, boot, install again and use the key, won't it work?