I was confronted with this situation recently. Team A lineman holds behind the line-of-scrimmage during a pass play. Continuing the same play quarterback rolls out to the right and throws a legal forward pass. While the ball is in the air, an inadvertant whistle is blown by an official. What is the proper ruling?

If the penalty is accepted, the IW is ignored.

If, for some reason, the penalty was declined, the down will be replayed.

I agree. Someone around here, don't remember who, always says best thing that can happen with an IW is a penalty. :)

NCAA replay the down, and if accepted penalty is enforced.
10 yards from the previous spot.

Accepted penalty prior to I.W.
 

Yes, if the penalty is accepted for a foul prior to the inadvertent whistle, you enforce the penalty and ignore the I.W.

Reminds me of my first year officiating. I think it was my first flag in a J.V. game. Working back judge, offense is on a long run towards the endzone, teammate clips an opponent, me throw flag and blow whistle while the play is in progress, me big-time red-face...

The coach asked me why I blew my whistle but he smiled because he knew the play would be called back anyway.