Most likely the filesystem is corrupted. If you haven't been changing things, MyDocs is FAT32 which doesn't support permissions, the permissions shown are what are assigned by the linux vfat drive based on the options specified when it was mounted, so if something is showing read-only it is most likely due to corruption.

To fix, since this partition is the one shared when you plug into a computer you can just plug it in to a Windows computer right click on the drive, select properties and there should be an option to check the drive for errors (these aren't exact instructions because I use Linux for day-today stuff and I can't be bothered to check).

Or to do it on your N900, open a terminal "sudo gainroot", then as root "umount /dev/mmcblk0p1", then "dosfsck -aw" to run the automatic check and repair, or "dosfsck -rw" for the interactive repair where you are asked what to do when the is more than one choice for how to repair the error, when that is done you can now remount it with "mount /dev/mmcblk0p1", when this is done you should now be able to remove the folder assuming it was left intact by the filesystem repair.