BAE-125-800XP Number 2 engine thrust reverser would not deploy while completing the Taxi Checklist. Maintenance had already deferred the Number 1 reverser; but failed to remove the Number 2 lockout device prior to returning the aircraft to service.

Narrative

The aircraft had been in maintenance for a left thrust reverser that was slow to deploy. Our mechanics at ZZZ deferred the thrust reverser; placarded it inoperative; and locked it out from functioning per our company MEL. After we started the aircraft and while completing the Taxi Checklist; we discovered that the right thrust reverser would not deploy either. We tried several times and it would not deploy. Our mechanics had locked-out both thrust reversers. We called our mechanics at ZZZ and they came right out to the airplane; observed the situation; and advised us to shut down the right engine. They went out to the right engine and removed the Thrust Reverser Lockout device. They instructed us to restart the right engine and perform the Thrust Reverser Check. The thrust reverser deployed as required. We then continued the flight to ZZZ1.There is no way the flight crew could have discovered this during an external preflight inspection. It was found during the Taxi Checklist. This could have been avoided if the mechanics would have removed the lockout device prior to return to service.