Pro/MECHANICA Motion requires to install a Microsoft C compiler on your system. Most likely you just forgot to set the MM_C_HOME environment variable after the installation. In order to avoid an unnecessary slowdown of your machine, wasted harddisk space etc. users of other C-compilers or users which do not program C at all might want to copy the "bin", "lib" and "include" directories from a colleague having a complete installation.
Don't forget to order/register your copy at DISTRILOG, as each license must be registered with the SIC.
Example (using the MS Visual C++ default path; include in autoexec.bat):
SET MM_C_HOME="C:\Program Files\Microsoft Visual Studio\VC98"
(Under WinNT/2000 you might want to use the "Environment Variables" dialog)