Melt the butter in a heavy medium saucepan over low heat. Add the onion, celery, red pepper, and Old Bay Seasoning. Cook, covered, for 10 minutes stirring occasionally. Add the stock and potato. Bring to a boil. Cook, covered, over low heat for 30 minutes or until the potato is very tender. Pureé in batches in a blender. Return to the saucepan. Add the half-and-half. Bring to a simmer. Stir in the crabmeat. Season with salt and pepper. Cover and turn off the heat. Let stand for 2 minutes. Ladle into soup bowls.