Character mistake: Watson says that there are fifteen windows on the front of 221B Baker Street, but if you look, there are only twelve.
Continuity mistake: In the basement of the Orpheum theater, Holmes takes a lamp off of a wall and places it on the floor. The shot cuts, and the lamp is back on the wall. When the shot cuts again, the lamp is back on the floor. (01:29:25 - 01:30:45)