If you upgraded your Shield to the 3.0 firmware, Android's usage of External Storage has changed and you no longer have permission to Write / Delete to all of External Storage IF it is formnatted as NTFS or (I believe) ExFAT.

FAT32 formatted drives (or in my case USB Sticks) can be written to as before.

For NTFS (and ExFat I assume), you can only write to files within a folder in Android/Data on the External Drive with the name of the Application that will be doing the writing, so in your case an ES File Exporer directory.