OK, finally I’ve managed it. As I said, my 12.1 installation is upgraded from 11.4. Now I found, that there was nspluginwrapper installed in 11.4, which is not available for 12.1. Despite absence in 12.1 repositories it was not removed during upgrade, crashing more recent icedtea-web version. Manually removing nspluginwrapper solved the issue.
Thx all for participation!
BTW is there any way to mark topics [SOLVED]?