Get the latest version of TurboActivate on your API page -- we've fixed the header compilation in C code a couple of months ago. Also, on Windows, make sure you're using the TurboActivate.lib file (see, Using TurboActivate with C, C++, and Objective-C):
#ifdef _WIN32 #pragma comment (lib, "TurboActivate.lib")#endif
On Linux, Mac or BSD you need to reference the libTurboActivate.so or .dylib in your compiler options. See "Using TurboActivate on Mac OS X" or "Using TurboActivate on Linux".