6.5.etc... requires a sessions folder within the ubbthreads directory to install. However, per this bug report, it's missing in the zip. You just need to create it and make sure it's writable. <img src="https://www.ubbcentral.com/boards/images/graemlins/smile.gif" alt="" />
Info:
https://www.ubbcentral.com/boards/showflat.php?Cat=&Board=UBB7&Number=42132
