Hmmm.... That's really weird. Are you sure it's the exact version of the mxunit plugin and mxunit framework? Is this running against ColdFusion and MXUnit locally, or is CF&MXUnit running on another server? The problem is either with the plugin or CF/MXUnit, and we need to isolate it. The plugin itself is kinda dumb... it draws the tree based on what it gets back from the server, and it looks like the server is sending back stuff to the plugin that it's not expecting.
As for your second question, to be clear: you mean that on your old setup, it was fine, but on the new one, it's not?