Toddw440

We've got a 04 Accord that we were not driving on a regular basis. It sat for about 3 weeks when I tried to crank it and found the battery dead because a light was left in. I charged the battery outside of the car and when I reinstalled it everything seemed fine except the check engine light is on and the immobilized light is flashing. I checked the code and it was p0603. I've ran thru the drive cycle and tried to reset and light stays on. I have no clue about immobilized light. What can I do? I've got to get emmissions done soon.