Hi Support.
Thanks for the suggestion but that did not help.
This is working now but the solution is not obvious from the error message generated.
It appears that if you want to run 2.6 of jfileupload you must have 2.6 of jsapi.jar.
Once I copied 2.6 of jspai.jar into my folder it worked correctly.

Hi, We are running successfully on 2.5 Beta 003. When we try to upgrade to 2.5 or 2.6 it throws an error about not finding CompressListener class. Why is that ? ---- network: Cache entry not found [url: https://fm.author-it.com/jfileupload/transfer/client/core/CompressListener.class, version: null] ...