The default location of the cache folder is webapps\qxpsm\cache (in the QPS Server application folder). If the cache folder is not present at this location, create a folder named 'cache' and restart QPS Server to register the changes. Verify the permissions on this folder.
Also, open the file 'Managerconfig.' (in the 'conf' directory inside the QPS Server application folder) and verify the location of the cache folder.