Symptoms

When trying to access the K2 designer site 'Sever Error Identity/STS/Windows Application'. This also resulted in another when navigating to the site via IIS directly: "Keyset Does Not Exist"
 

Diagnoses

There was a congifguration issue regarding STS in the HostServer.Config.
 

Resolution

To resolve this issue you must delete the variables within the 'STS' variables within the HostServer.Config table. These variables should be the following

1.) STS_Certificate
2.) STS_Thumbprint


- Reconfigure the K2 Workspace component via the set up.

What this should do in turn is create new certificates and update the variables upon the DB as well. New thumbprints should be generated for the STS Web Config, Certificates store and DB.