We are just upgrading to 6.5.2, with latest PSOToolkit as well. In one of our previous discussions, you mentioned there is a new getParentFolderPath() method. This new method takes $sys.assemblyItem as a parameter and computes the parent path for the current folder. (All this will help me deal with paste-as-link issues.)
However, my version of tookit still has only the original method (itemguid as param). There’s nothing else in psoFolderTools class?
What is the build number of the toolkit? (open the jar with WinZIP or something similar, and look for the build.properties file).
Also check that you have only 1 PSOToolkit jar. Somewhere along the way, the name changed (especially if you upgraded the system), and you need to remove the old JARs from the lib directory.