Error 20 on Canon 450d

Recently some water got inside my camera and I had to disassemble it and clean it. The final casualty was that the clock battery (MS614SE) had been damaged and I had to buy a new one. Including the shipping fee the repair cost was $4.

However, after the assembly when I tried to make a photo I got:

Err 20
Shooting is not possible due

to an error.
Turn the camera off and on

again or re-install the

battery

The solution turned out to be simple: unscrew the long screw next to the zero mark and replace it with a short screw. The fix works because the long screw is mechanically blocking the gears inside.