Here are all important links:
http://lmms.io/forum/viewtopic.php?f=1&t=4740
-A few rules and useful forum instructions
If you like to introduce yourself, to the community, go here:
http://lmms.io/forum/viewtopic.php?f=4&t=4480
It is written on the VST-UI
Here the plugin Synth1 is used

But the picture is from a working project. If the project or its paths has been corrupted, the it will show: "No plugin loaded"
Is that the case
Are you familiar with programming, and the format XML?
You should be able to readout the VST inside the XML of a <project>.mmp file.
If you only have a .mmpz, then sorry, but you cant