Hi,
but the license for the beta versions is active only for 30 days?
You don't say what avast version you have or how you installed the beta version ?
If you did a clean install of the beta, then it would be running effectively in trial mode until you registered or applied your license/activation code. That said 30 days in most cases should be enough to see the beta through to completion. This particular beta2 build has only been out a week.
Even if the overall duration is more than 30 days, it will probably be OK after that.