When you Rt-Click on a VSM, and try to deploy the model to a VSE server, Deploy/Redeploy to VSE@default Option is disabled in the Workstation.
All supported DevTest Environments
If VSE server is not running, Deploy/Redeploy to VSE@default Option will be disabled / grayed out.
If there is a firewall issue this will cause the same issue.
Start the VSE Server, this will enable the Deploy/Redeploy to VSE@default option in the Workstation and you should be able to deploy the VSM.
If the VSE is running and still getting the issue, it is probably due to a firewall. Make sure all DevTest ports are open to not only send but receive data.