Can't delete/edit files on my pendrive

If I were to guess it sounds to me like your Pendrive is corrupted. the simple solution is to back-up and reformat however if you want to find out if it is really corrupted or not which could be a sign of a failing flash drive use fsck

first back-up your pendrive/card then find out what mount point its under eg. /dev/sdb , /dev/sdc etc.

You can find this information in disk utility under the heading Device:

in the screen shot it is /dev/sdb1

You can then modify these commands and run each

sudo umount /media/disk

sudo fsck -favVr /dev/sdb1

Alternatively you can click "check file system" after unmounting the drive in disk utility

Edit:

I have found another solution to this problem the steps are as follows

1. Mount the USB Drive you are having the problem with
2. Open Disk Utility as root open a terminal and enter gksu palimpsest
3. Unmount the Drive and remove
4. Plug it back in

Hopefully this will work if all else has failed