You have to run DiskPart to fix the drive ReadOnly error. Make sure your drive is plugged in and then start the utility by typing diskpart in the Start > search for programs or files box. Left click once on diskpart.exe to start the utility.
Once the utility loads, follow the steps in this Forum post to remove the ReadOnly status from the drive / volume (it must be removed from both).
Microsoft DiskPart version 6.0.6002 Copyright (C) 1999-2007 Microsoft Corporation. On computer: DELL755DISKPART> list disk
Disk ### Status Size Free Dyn Gpt
Disk 0 Online 233 GB 0 B
Disk 1 Online 112 GB 0 BDISKPART> select disk 1
Disk 1 is now the selected disk.
DISKPART> list volume
Volume ### Ltr Label Fs Type Size Status Info
Volume 0 D DVD-ROM 0 B No Media
Volume 1 C NTFS Partition 233 GB Healthy System
Volume 2 E UNTITLED FAT32 Partition 112 GB HealthyDISKPART> select volume 2
Volume 2 is the selected volume.DISKPART> detail disk
Maxtor OneTouch III USB Device
Disk ID: BA52D44C
Type : USB
Bus : 0
Target : 0
LUN ID : 0
Read-only : Yes
Boot Disk : No
Pagefile Disk : No
Hibernation File Disk : No
Crashdump Disk : No
Volume ### Ltr Label Fs Type Size Status Info
- Volume 2 E UNTITLED FAT32 Partition 112 GB Healthy
DISKPART> detail volume
Disk ### Status Size Free Dyn Gpt
- Disk 1 Online 112 GB 0 B
Read-only : Yes
Hidden : No
No Default Drive Letter: No
Shadow Copy : No
Dismounted : No
BitLocker Encrypted : No
Volume Capacity : 112 GB
Volume Free Space : 75 GBDISKPART> attr disk clear readonly
Disk attributes cleared successfully.DISKPART> attr volume clear readonly
Volume attributes cleared successfully.DISKPART> detail disk
Maxtor OneTouch III USB Device
Disk ID: BA52D44C
Type : USB
Bus : 0
Target : 0
LUN ID : 0
Read-only : No
Boot Disk : No
Pagefile Disk : No
Hibernation File Disk : No
Crashdump Disk : No
Volume ### Ltr Label Fs Type Size Status Info
- Volume 2 E UNTITLED FAT32 Partition 112 GB Healthy
DISKPART> detail volume
Disk ### Status Size Free Dyn Gpt
- Disk 1 Online 112 GB 0 B
Read-only : No
Hidden : No
No Default Drive Letter: No
Shadow Copy : No
Dismounted : No
BitLocker Encrypted : No
Volume Capacity : 112 GB
Volume Free Space : 75 GB
DISKPART>You have to remove the read only status of the disk before you can remove the read only status of the volume
Notice that the example selects both the disk and the volume. Again, if anything is not clear to you, come back and ask.