For some reason Akai MPC is not always registering the VST folders. Please make sure these two folders are listed in the preferences:
- for 32 bit VST support on windows: C:\Program Files (x86)\Common Files\Steinberg\VST2
- for 64 bit VST support on windows: C:\Program Files\Common Files\Steinberg\VST2
Make sure to press the rescan button.