Why can't I assign the left shift key to crouch?

[Prince of China]

In common controls, I can assign the left shift key to other actions, but not crouch. It says that a duplicate key was found in helicopter controls, but when I checked, no action used the left shift key. Can anyone help?

 

[AiM]

Manually edit it in your config.con file

My Documents/BF2/0001/config.con

Go Go Go!

 

[Prince of China]

Okay, thanks.