I dunno if it's "official," but the rogue in my group actually opted out of having his sneak attack apply to every hit in a round, when I would have let him take it.
But, we came up with a "house" rule (I guess, unless it turns out to be "official") that the first hit on an opponent can have sneak attack applied to it, and if another opponent is attacked in that same round, then sneak attack can be applied to the other opponent as well.
So, basically, you can sneak attack an opponent once per round, but you can sneak attack more than one opponent per round.
Then your DM is ruling it wrong. The Rogue already has the worst BAB progression in the game, sneak attack is the Rogue's main damage dealer against the bad guys. If the DM takes that away, he is basically stripping the Rogue of the one thing that makes him so deadly.
This ruling on Sneak Attack is "Official". It is published in the PHB and again on the WoTC SRD. If your DM continues to rule the sneak attack damage this way, he is cheating you out. Your DM should really double check his interpretation on these things if he is unsure on how to adjudicate these things.
Yes TWF and Sneak Attack can be nasty (especially at higher levels), but in truth the odds are that a TWF Rogue will rarley hit while TWF at higher levels.