Volatility plugin error: Invalid module

I've been trying out Volatility and am getting an "Invalid module" error when I try to use it with plugins that I have downloaded

C\Volatility-1.3_Beta>C\Python25\python.exe volatility keyboardbuffer -f mymemory.dd

Error Invalid module [keyboardbuffer].

I tried placing the plugins in the same folder, using different python releases, and compiling the py file with the release I am using, but still no luck.

I also googled the problem to see if anyone else had the same problem & I found a couple of listings, but none with any solutions.

Does anyone have an idea of what I may be doing wrong?

(Also, Volatility no longer works at all using Python 3)