This is a known hardware error and can’t be fixed. Sandisk is aware of the issue, although there is no official recall for the product. This is an offical answer if you contact customer service:
"I understand that you are getting write protection error while accessing your Cruzer flash drive. The flash drive has detected a potential fault and has become write protected to prevent data loss. There is no method to fix this. You will need to backup your data and replace the flash drive.
Our team of developers is in combination with the OS developers looking into a solution to resolve this issue.
Please note that only a minor percentage of users are experiencing the write protection issue and these are the customers posting on the internet to find a solution."
SOLUTION 1: Return to where you bought and get a refund (as others usb drives might have the same issue)
SOLUTION 2: Contact Sandisk costumer service and get a refund, for the same reasons