Symptoms
Trying to build a K2 process flow within Visual Studio 2010 and receive the following error 'Root Element is missing.'. Attached is a screenshot from Visual Studio.
Diagnoses
After the change was made, the K2 workflow needed updated.
Resolution
When you open the process where the change was made, right click on the design canvas and select “Update design Templates”, re-deploy and test. Please bear in mind that any custom code behind an event other than server event will be discarded, so it will be a good idea to make a copy of all your custom code.