I also ran into this problem every now and then in the past, and restarting the phone used to work... but this last time restarting the phone did NOT help, and the camera was completely useless.

I found a solution - thanks to the folks at Qik who suggested it might be a hard drive problem. I had to run a scan disk on the memory through my windows machine. After I ran it and fixed the errors, the camera worked again.

These are the steps I took to fix the problem:

1) Connect your phone to a Windows machine through USB.

2) Set the phone to "USB Mass Storage" mode, and wait for it to show up on windows explorer.

3) Right click on the drive and select properties. Go to Tools tab, and under error checking, select "Check Now...". Select both options (automatically fix and attempt recovery of bad sectors).

4) Click start, wait for a while.

So now I am worried. This weekend with my girlfriend, I totally missed some awesome picture taking opportunities, and I can't rely on this N900 camera because I never know when it might not work for me. I hate to have to bring a separate camera (the camera pictures look great... when it works).

Does anyone know if there is there a linux command I can run to do a scan disk/fix disk from the x-terminal? At least that way when the camera breaks, i can fix it without having to wait till i get home. My iPhone friends will laugh at me though if I have to reformat my hard drive ever time i want to take a picture.

:S