Hi sab57
I'm not with Laminar Research, just a fellow simmer in the UK, but please could you confirm whether you purchased your copy of X-Plane 11 from the LR website, LR DVD or from Steam?
If you purchased it from LR, then please in the first instance look in the following directory to see if the Sikorsky S-76C folders and files are where they should be:- C:\X-Plane 11\Aircraft\Laminar Research\Sikorsky S-76
Regards