What happens if you told a free thrower shooter he/she had two shots, but it really was a one and one, and you, the official, grab the ball after he/she missed the free throw. Is this a correctable error and does he/she get to shoot it again? What is the correct procedure for handling this error?

The first thing you do is get together with your partner(s) and slap each other so that you're both now fully awake. :D

This is not one of the correctable errors listed in 2.10 I'd say that you basically have the same thing as an inadvertant whistle here. Nobody had possession so go to A.P.

Z

I think does fall under the correctible error rule, since it's essentially awarding an unmerited FT.

I agree with Z that you go to the arrow to resume play.

Lotto,

This is not a correctible error as defined in rule 2.10. The free throw that was taken was merited. Since it missed, no more free throws are to be awarded. So the correct number of free throws were awarded.

What was done incorrectly was that the official interrupted play. Go to AP because of the official's error, but this is not one of the correctable errors as listed under 2.10.

Z

Case book play 8.6.1 is close enough and gives you the general principles to use.

OFFICIALS PROVIDE ERRONEOUS INFORMATION
8.6.1 SITUATION: A1 is about to attempt the first of a one-and-one free-throw situation. The administering official steps in and erroneously informs players that two shots will be taken. A1's first attempt is unsuccessful. The missed shot is rebounded by: (a) B1, with all other players motionless in anticipation of another throw; (b) A2, with all other players motionless in anticipation of another throw; or (c) B2, with several players from both teams attempting to secure the rebound. The officials recognize their error at this point. RULING: In (a) and (b), the official's error clearly put one team at a disadvantage (players stood motionless and didn't attempt to rebound). Play should be blown dead immediately and resumed using the alternating-possession procedure. In (c), both teams made an attempt to rebound despite the official's error and had an equal opportunity to gain possession of the rebound. Play should continue.