This is a problem I had, and most of the responses on google were in the form of mailing lists, uggh.
Anyway, I did this reading so you don’t have to, first thing to try:
Did you spell the generator correctly? type cmake with no arguments, see if your generator is listed, if so, are you spelling it exactly? Try again.
If you have messed around with this for awhile, you might need to del cmakecache.txt file.
Hope this helps someone else when they have the issue. And remember kiddies, don’t count on people spelling their directions correctly.