Anyone who is having this problem just connect your n900 with your windows pc in mass storage mood and a window should popup with dialoudge "scan for fix file system error" or similler, click on that and wait. If no window popup, than right click on n900 drive and go to properties then go to 'tools' tab and click "check Now" then click 'start' and wait. After the work done, your n900 now should have the ability to delete those files or folder its could'nt before.