I went to pronterface, ran G28.
when I sent G29 n 2 i got this error message:
This is a problem with the GCode protocol. You can't send a capital N because that says what line of GCode was transferred. That is why a lower case 'n' is used. But because it was causing so many problems (like you just ran into), the parameter was changed to 'P' in the new code.

(If you look at what the error code says... You actually sent a Capital N. Probably a lower case 'n' would have behaved as expected.)