Which version of C3 are you using? For this plug-in, I recommend the latest beta. Some of the earlier C3 stable versions did not have the latest C3 SDK which this plug-in depends on.
Sorry you are having an issue, which version of the addon are you using? There are two different versions posted. If you are using a 2.x version, try downloading the project again, I have heard that works for people sometimes.
