Have a look at this:

http://discussions.europe.nokia.com/...1ECE4DF649DD15


There's a test to see whether the keyboard sensor works. Also the last post on that thread offers a possible solution that might be worth trying:

Hey guys, had the same problem. Turned out the solution for me was the following:

-> Turn off virtual keyboard
-> Turn off the phone
-> Turn on the phone again
-> Turn on virtual keyboard

...and it worked. Good luck!

Scigi