I believe it is stating that your java (Tomcat, WebSphere, etc) cannot find a "class" definition that it needs. Unfortunately, the error is not very specific. If there are details which identify the missing class, check/reset permissions on that class. If there are no details, welcome to my world!! You're just going to have to sleuth around your system and log endless calls with Cognos till you identify the issue.
-Cindy