What actors and actresses appeared in The Mystery of the Snakeskin Belt - 1951?

You're likely thinking of "The Strange Door" (1951), not "The Mystery of the Snakeskin Belt".

"The Strange Door" stars:

* Charles Laughton as the sadistic, vengeful Baron de Martel

* Boris Karloff as the vengeful, murderous sorcerer, "The Executioner"

* Cathy O'Donnell as the innocent and pure, Marie Roget

* Michael Rennie as the courageous and noble, Jean de Valois

There is no known film called "The Mystery of the Snakeskin Belt". It is possible you are misremembering the title or perhaps a different film altogether.