Lameness caused my bell boots

My 8 year old gelding goes lame when you put bell boots on him. It seems to be the right front only. what can be causing this?

Discontinue the use of the boots as they may not fit and may be causing the discomfort that you are seeing.
   
Check his feet. He may have a puncture wound or bruising on his foot and check for heat on the hoof wall and sole. Also check for swelling and heat on the leg. If you find an injury treat accordingly but if unsure call a vet.
   
What degree is he lame to? is it just a shortened stride on his forelimb or is it so bad he cannot put weight on it? If you cannot pinpoint the cause of lameness or he deteriorates call your vet immediately. IF IN DOUBT CALL YOUR VET.

There are no cuts, the farrier looked for bruising and soreness on the hoof and sole, none of that, there is no swelling or heat.
   
He is lame to the point where he is unrideable. But he needs bell boots when the time comes for him to get shoed again.