Hi,
thank You for Your answer.
I've installed Avast on clean home dirs ie. always remove .avast directory before another try.
BTW. I went to avast reg page and requested to resend me key second time ( choose "I'm a registered user, but I lost my registration key" option assuming maybe mail was malformed on the way to me
??). I was sent with the same key (obviously) but it didn't help.
But after two days I was sent mail from avast with another key ( I've never attempted to obtain another one ! ). This is completely different key and I gave it a try. And it works.
Weird..... I still wondering why I was sent another key without any word of explanation.
Nevertheless , the main problem was solved
Regards
Marcin