Today when i started doing my pull ups routine i felt an immense pain in my arms and i couldn't do only 1 set.can you tell me the cause?

Muscle injury?: I would need to know more information like has this happened before, did you suffer any injuries before this happened, etc?but to make a good guess based on the information you are providing, this could be a torn muscle or tendon probably related to the same exercise you are doing. Rest it for now, ice the area and if not better in a couple of days or severe pain now see your doctor.