A couple of approaches are possible here if you really do not wish all the (very substantial) benefits of upgrading:
1. Make sure Tools > Preferences > Database > Advanced Parameters > Use OCI/Thick driver is unchecked
2. If you require OCI/Thick, the OJDBC driver version SQL Developer should use is from Oracle client in PATH var.
I believe SQL Developer 1.5.5 ships with only a jdbc\lib\ojdbc5.jar. It will attempt to find an ojdbc jar that comes from an installed Oracle client, but often won't pick up the correct version. For example, on my Win 7 system, if my PATH var points to the 18.104.22.168 full oracle client, I can connect with OCI/Thick enable. If I switch PATH to point an an 22.214.171.124 instant client, however, SQL Developer still finds the 126.96.36.199 ojdbc driver (see Help > About > Properties > jdbc.library value) and I get the t2cSetSessionTimeZone error when using OCI/Thick. One option is to copy the client's ojdbc6.jar into the SQL Developer jdbc\lib directory and start SQL Developer from a bat file where the Oracle home is set as 1.5.5's top level sqldeveloper directory.
Good luck (but I strongly recommend upgrading!),
SQL Developer Team
Message was edited by: Gary Graham