Enterprise Portal Error (Cryptographic initialisation vector has expired)

Hi All

Upon launching the Employee Self Service Home Screen for enterprise portal as user Admin I get the following error:
“WebSession.parseArgs: Cryptographic initialisation vector has expired”

The event log shows the same error. But states the Dynamics Object Adapter Failed.

Has anyone encountered this issue before? I have done an IIS reset, checked permissions for the object adapter and eveyrthing seems fine!