After upgrading Workflow on a server, and then attempting to open the portal, the below error was obtained.
After upgrading, the Processmanager Webpage/Application was changed to use the DefaultAppPool in IIS, rather than the custom app pool that had been previously configured.
Open IIS, find the ProcessManager Application Website, and reset it's application pool to the previously configured app pool. Please note that the ProcessManager, SymWebInclude, and SymWorkflowPages web applications/pages must all be in the same application pool.
Servicedesk 7.1 Sp1