Symptoms

Unable to validate user
 

Diagnoses

We have created a form and workflow using the K2 Designer and when we reach the point at which you can specify an identity under which the event executes, we opt to configure credentials. No matter what account we choose, we receive a Warning popup box saying "Unable to validate the user name" followed by 0000000-0000-0000-0000-00000000000 on the next line.
 

Resolution

This has been confirmed as a bug and extends past the SP designers as well.

At this stage the only workaround is to use either k2 studio or k2 for visual studio.