Hi Newbee,
Can you try using the "full name" in your declaration? E.g.:
extern const ti_sysbios_knl_Semaphore_Handle mySem;
Also, which files are you #include-ing in your file?
Finally, you may want to look at the example called 'bigtime.' This example is a C++ example, which defines a Clock class and uses Semaphores within the code. I was able to compile that example without any issues, can you give it a try, too?
Steve