Hi! I have the same problem,
and no idea what to do.
To test what could be wrong, i have downloaded the codelab plugin source code. (because that plugin was already working in my PDN)
I have build the solution in my visual c#, and moved the new codelab.dll to /effects, and wth? PDN doesnt show the codelab plugin anymore. When I move the old one back there its in the effects menu again.
I have compared the bytesize of the original codelab.dll , and my new rebuilt codelab.dll and it is exactly the same, thats whats realy weird about that x.x
Any ideas? D=
EDIT!!:
K, i have changed solution to .net 3.5 and restarted my computer -> worked!