Hi,
thanks for prompt response. I haven't seen how my gf uninstalled trend micro, so I restored the system from recovery partition. The tool from the website you recommended did not worked, however, very similar was included to trend micro package, which remove the software.
After reboot I was able to register Avast without problems. Unfortunately, after 2 or 3 restarts the same happened. So it doesn't look like Trend is to blame. The most annoying thing is that Chrome is locked too ;/
What else can I do? I've been using Avast for years now. I got it on another Win7 PC and runs without problems.
Sorry for reincarnation of old topic, but it looked like this is the same issue.