Blowing fuse

Hopefully somebody here will be able to help.

I have a 2000 A160 Avantgarde with the auto clutch, and the reversing lights are not working. I have discovered that fuse no. 39 was blown. I replaced this and it has blown straight away. Would a blown bulb cause this to happen or would it lead to a more serious problem like the reversing light switch?

Please help as i know i don't need reversing lights for an MOT but would like to have them working.

Thanks
Steve