Problem: User is receiving a correlation ID when trying to access a PWA of a newly migrated site. This problem was limited to 2 sites in my case.
Resolution: After discussing with my Project Server colleague, this can occure on project sites exported from Project Server 2007 and imported into Project Server 2010 when they do not have an associated project under Server Settings > Project Sites. We found in this case that the project site had no associated project plan. The project name had changed from the 3346 name included in the project site to 1995; the 1995 project plan existed but had no project site. We imported the project site using stsadm –o import –url –filename to a new site with the new 1995 name and then created the association of this new site with the existing 1995 plan. We knew we were successful when the associated save worked. Next step was just to publish the plan and make sure the jobs processed successfully.