Look at the UD log. There will be a log entry on why is isn't mounting. Probably a permission (credentials?) issue.
I clicked on the Log button on the right but nothing appears in the Unassigned Devices Log. I'm able to get into the share from my Windows PC, and the plugin did find the share after I put in my user and pass for that share (located on the Windows PC) but still doesn't mount.
Did you let UD find the server and share, or did you manually enter it?