MDT ACFT HAD DOOR LIGHT ON THE RED WARNING PANEL DURING TKOF; ABORTED. FLC TAXIED BACK; MECHS CHKED IT AND SIGNED IT OFF. NEXT TKOF ROLL THE LIGHT CAME ON AGAIN WITH A RESULTING ABORT. ACFT TAKEN OTS FOR REPAIR. THE ACFT HAD BEEN USED FOR TRAINING AND EMER EXIT REMOVAL PRACTICE.

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AFTER A 1 1/2 HR LAYOVER IN PITTSBURGH BTWN FLTS; I RETURNED TO THE ACFT; PERFORMED A WALK AROUND; FOUND EVERYTHING SATISFACTORY AND PREPARED FOR DEP. ON THE TKOF ROLL A 'DOOR' RED WARNING PANEL LIGHT ILLUMINATED FORCING ME TO ABORT TKOF. AFTER RETURNING TO THE GATE; MAINT EXAMINED THE ACFT EMER EXIT IN QUESTION; TAXI-CHKED THE PLANE AND SIGNED OFF THE WRITE-UP AS GOOD IN THE MAINT LOG. AS WE TAXIED OUT AGAIN; ALL COCKPIT INDICATIONS WERE NORMAL. ON THE TKOF ROLL THE RWP LIGHT 'DOORS' ILLUMINATED AGAIN FORCING ME TO ABORT AGAIN. THE MECHS WERE TEARING APART THE COMPUTER PANEL WHEN I LEFT THE ACFT. I FOUND OUT LATER A RECURRENT GND SCHOOL CLASS HAD BEEN USING THE DOORS FOR EMER EXIT REMOVAL PRACTICE DURING OUR BREAK. THEY ALL APPEARED TO BE REPLACED CORRECTLY WHEN I PERFORMED MY WALK AROUND AND THEY WERE ALL CLOSED ACCORDING TO THE DOOR PAGE ON THE MULTI FUNCTIONAL DISPLAY IN THE COCKPIT; AS WELL AS ON THE RED WARNING PANEL. IT WAS RAINING PRETTY HARD DURING OUR BREAK SO I DON'T KNOW IF A SENSOR WAS AFFECTED BY MOISTURE OR IF THERE WAS A MALFUNCTIONING COMPUTER CONTRIBUTING TO THE PROB. I FEEL THAT THERE WAS NOTHING MORE THE CREW OR I COULD HAVE DONE TO AVOID EITHER REJECTED TKOF.