Connection to 11g database just hang. (4243582)

After database maintenance/reboot suddenly TOAD version 9.0.1 stopped working with existing Oracle database 11.1.0.6.
I downloaded a new version of TOAD 10.6.1 and also installed Oracle client 11.2.0.1 on my PC. However still it has connection problem.
TOAD has no issues connecting to other databases which are on same version of Oracle database 11.1.0.6 on other test servers.
The only database TOAD has is hanging on when trying to connect to is our Production database.

After TOAD hangs during DB connection - I killed the toad session from another tool SQL*developer. As soon as I killed the session (using alter system kill session command) I saw another new active sessions from Toad, at this time also toad was not responding. So I killed that new session too. Now this time immediate after killing the session Toad was connected to database and I was able to use it without any issues.