This problem may be caused by importing a View that includes a custom sort. To confirm if this is the case launch Open Workbench, and right click on the View in your Library. Click "Edit".
On the "View Definition" screen go to the "Sort" tab, and see if any fields are present. If so you will need to delete and recreate the Sort.
Release : Any
Component : CA PPM APPLICATION
The Documentation for Open Workbench and how to create Views is located here: Display Project Plan Data in Open Workbench Views