Exactly the same thing happened to me. I'd found stage 1 of a multi, put S2 co-ords into gmm, then couldn't find the cache anywhere. Turns out gmm wanted me to search in the middle of a road nowhere near GZ. I've added my comments to the google mobile help forum, I suggest anyone else who has this problem does the same, more voices have to help!
Google Map Mobile help topic, add your comment here!