Symptoms

Could not load file or assembly 'SourceCode.Forms.Utilities' when opening a workflow
 

Diagnoses

In K2 Designer when I try to open my workflow I get "Could not load file or assembly 'SourceCode.Forms.Utilities, Version=4.0.0.0, Culture=neutral, PublicKeyToken=16a2c5aaaa1b130d' or one of its dependencies. The system cannot find the file specified."

When I click OK on the error the Workflow Validation Screen hangs and I am unable to do anything with the workflow.
 

Resolution 
This usually happens if you're running K2 with a separate web server. There's a couple ways you can address it if that's the case - you can simply install K2Studio on your web server - which might be the easiest and quickest solution, though not very clean. You can also manually add the dll to the gac on your web server. They are found in %program files%K2 blackpearlin and need to be copied to c:windowsassemblies on the web server.