Are all the network connections on all nodes (and witness if applicable) seeing the network as "domain"? I have found in the past differing network recognition has caused the issue...
Also, while on the subject of clustering, I would like to share a VBScript that I wrote that will display the status of the cluster... It will list which Applications...
In my experience, in a test environment, it is ok to shutdown the offline node, then the online node, then the DC. In a production environment, it would be best...