I had the same problem, updating the dll a few times with a few different builds didn't work, still got nothing. Then I paid closer attention to the error message from build 197 (retrieved from above link... Thanks!!!) Your mileage might vary, depending on your OS and settings, but this worked for me in Win 8.1 Pro, and Win 7 Pro. Open the mechjeb2.dll properties: at the bottom of the window may be a note about the program originating from another computer. Unblock it, or it won't load. I unblocked the files for the pod part as well. Once done build 198 from the above link worked great. You might have to do the R&D too, depending on if you played with too much trying to get it to work. again, ymmv.
