sounds like its not installed properly. to be fair, ive never used fl, but i assume its the same in the sense that you have to have the dll in the right place. id reinstall and make sure the .dll is in the vst folder (if thats how fl works)
Were you able to successfully activate it through N.I. Service Center?
The thing with Native Instruments (and other heavy protected products like Waves) is that they're super tight with their registration process. If your mate had an extra code, I'll assume that he got possession of the extra code because he either had Massive and bought a copy of Komplete 8 (which comes with Massive) or he had a copy of Massive and bought the Maschine MKII (comes with a free copy of Massive). In either of these cases, the code should work when activated through Native Instruments' Service Center app.
The other issue could be your version of FL Studio. Make sure that it's both legitimate and up-to-date.
Prior to dropping the cash for the upgrade, I would contact either (or both) Native Instruments and Image-Line to inquire about what could be causing the error when trying to initiate Massive with FL Studio. Also, check the forums on both sites, nine times out of ten you're not the only user with this issue and perhaps someone else who had the same problem has a solution.