theft system light....engine dies

I recently had to replace my key lock tumbler on a 1996 cavalier. After replacing it, the engine will start fine and then immediately (2-3 secs) die. Then the "theft system" light starts blinking on the dash. Does anyone know what could cause this?

There were two areas that I thought could be the problem. First, there is a wire from the tumbler that goes somewhere up into the dash. I cut that wire in order to remove the old tumbler and merged the wiring together. But it doesn't seem that this wire has anything to do with the actual engine dying. Second, there is a long plastic piece that connects the tumbler to the ignition switch. Maybe this piece is not engaging the ignition switch properly? Any help is greatly appreciated because the next alternative will probably be expensive.

Thanks,
Rick

need to re-code your car - passlock still looking for the old resistance value..... Dlr can help w/ that.