Ben Plont quoted Wikipedia in the comments:
Tyler tries to escape by deactivating the bomb on the tunnel gate, but discovers that it has been tampered with so it goes off rather than disarms when he leaves.
However, that part is currently written a bit differently:
Tyler tries to escape but encounters the tunnel gate bomb. When he tries to deactivate it, it detonates instead, killing him.
In my opinion, there are two important details:
Tyler did not set the bomb himself. He sets up a camera and then gets the bomb out of the protective suitcase, gives it to one of the henchmen, asks "You guys are good?" and leaves commenting "Don't mess it up".
Raphelson, who was actually the man behind it all, wanted to eliminate all the evidence (including witnesses). Keep in mind that he was more than likely getting some operational help from his buds from the weapons industry.
So, my guess is that the bomb was deliberately planted in a way that it explodes whatever you do with it. Was it prepared like that before they even went in there or was it done there by the guy who planted it, remains unclear. But, with the lack of other viable explanations, I'd say it was part of the plan not to allow anyone to get out alive.
In my opinion, this is the weakest part of the movie. Not that any of that other stuff is realistic, but it works fine in the movie. This scene, however, is confusing. I believe that it was done to quickly get rid of Tyler when the movie didn't need him anymore, and you cannot just shoot a guy that wields computers instead of guns. This is quite similar to Argile disposing of Theo in "Die Hard", by crashing into his ambulance with a limo, thus not directly killing him, but only incapacitating him.