Q:

Disk on key is read only on every computer

I have a 16 GB SanDisk Cruzer Blade Disk-on-key.
After a few days of use, it has become write-protected/read-only.
When I plug it in, you can see this in my Ubuntu's dmesg:
[  819.003359] usb 2-5: new high-speed USB device number 5 using ehci-pci
[  819.136249] usb 2-5: New USB device found, idVendor=0781, idProduct=5567
[  819.136257] usb 2-5: New USB device strings: Mfr=1, Product=2, SerialNumber=3
[  819.136261] usb 2-5: Product: Cruzer Blade
[  819.136265] usb 2-5: Manufacturer: SanDisk
[  819.136269] usb 2-5: SerialNumber: 4C530210071007116494
[  819.136891] usb-storage 2-5:1.0: USB Mass Storage device detected
[  819.137024] scsi8 : usb-storage 2-5:1.0
[  820.136696] scsi 8:0:0:0: Direct-Access     SanDisk  Cruzer Blade   2.01 PQ: 0 ANSI: 6
[  820.137150] sd 8:0:0:0: Attached scsi generic sg3 type 0
[  820.138497] sd 8:0:0:0: [sdc] 31266816 512-byte logical blocks: (16.0 GB/14.9 GiB)
[  820.142194] sd 8:0:0:0: [sdc] Write Protect is on
[  820.142204] sd 8:0:0:0: [sdc] Mode Sense: 43 00 80 00
[  820.144629] sd 8:0:0:0: [sdc] Write cache: disabled, read cache: enabled, doesn't support DPO or FUA
[  820.156667]  sdc: sdc1
[  820.159903] sd 8:0:0:0: [sdc] Attached SCSI disk

You can see that is says that write-protect is on.
I've already tried:

Looking for a read-only hardware switch
Using Gparted to format the drive. It says that the drive is read-only so it can't write to it
Using dd to overwrite the drive with 0s. It also can't open the device (/dev/sdc) for writing.
Pluging it in to a Windows 7. It too says it's read only

I did find this thread on Sandisk's forums.
Does it mean that this has no solution? Must I just throw the Disk on Key after a mere days of use?

A:

I've contacted SanDisk, and they've said it happened "beacuse the flash drive has detected a potential fault and became write-protected to prevent data loss. There is no method to fix this."
They've offered to replace it if I send it to them on my own expense.
They are, as it turns out, aware of this problem.
I, however, chose to switch to another company's disk-on-key.
Thank you.

A:

[ 820.142194] sd 8:0:0:0: [sdc] Write Protect is on

At least some flash storage devices (such as SD cards) do have internal write protect settings, including a permanent write protect bit.  I first heard of this here, and don't know if it could apply to your device, but if you could not dd with root privileges to a USB stick then it would seem to be a hardware lock.
However, if this was done intentionally by, e.g., some Windows safety mechanism, it's unlikely that would use the permanent bit (if any).  
Try:
sudo hdparm -r /dev/sdN

Where sdN is the correct device node.  You will probably get:
/dev/sda:
readonly      =  1 (on)

Note that you may have to install hdparm first (search for a package with that in the name).  You can try to change this setting with:
sudo hdparm -r0 /dev/sdN

This should set the "readonly" option to 0 (off).  For more details consult man hdparm.

