Thanks for interesting suggestion. Unfortunately this seems not to be cause of my problems:
ls -l /dev | grep random
crw-r--r-- 1 root system 37, 0 Apr 09 10:14 random
Server, running AIX 6.1 developed strange problem when logging in via SSH -- ssh client hangs without any error.
It is possible to run commands on server, using ssh ("ssh servername ls -l" is OK)...