Android Camera App complains "Please insert an SD card..."

Today my Android phone running Oxygen Rom 2.3 could not make photos any more. A error message appeared on opening the camera app: "Please insert an SD card before using the camera", although the sd card was present and also detected by the system.

When mounting it on my Linux system, I could not delete any files and the error appeared: "read-only file system".
A little research revealed, my fat32 filesystem got corrupt somehow, but this can be easily fixed:

sudo fsck.vfat /dev/mysdcard -v -r

(please unmount the partition before and change /dev/mysdcard to the value of your device! you can see all your mounted partitions with running the "df" command!)

On Windows, there might also be a button somewhere saying "Repair File-System".
Mount SD card, boot the phone and it should be fixed!