One Tumble skill use requires a check (DC 25) to do this:
Tumble at one-half speed through an area occupied by an enemy (over, under, or around the opponent) as part of normal movement, provoking no attacks of opportunity while doing so. Failure means you stop before entering the enemy-occupied area and provoke an attack of opportunity from that enemy. Check separately for each opponent. Each additional enemy after the first adds +2 to the Tumble DC. (Player’s Handbook 84)
Abe the Medium human rogue is 10 ft. from his opponent, Bob the Medium human fighter who wields a longsword. Abe takes a move action and uses 10 ft. of his speed 30 ft. to become adjacent to Bob. Then Abe makes a Tumble skill check as described above to move through Bob’s space, fails the Tumble skill check, provokes an attack of opportunity from Bob, and stops before he enters Bob’s space.
Does Abe’s failed attempt to enter Bob’s space flat-out end Abe’s move action? Or does Abe’s failed attempt to enter Bob’s space consume 10 ft. of Abe’s speed, and Abe can spend his remaining 10 ft. of speed as he wills? Or does Abe’s failed attempt consume none of Abe’s speed—as Abe didn’t actually enter Bob’s space after all—, and Abe can spend his remaining 20 ft. of speed as he wills? Or is there another outcome that I’ve not listed here?