1) - Does it have a protect/unprotect slider on the unit ?
2) - Have you tried formatting the drive ?
3) Use regedit to apply a registry tweak to enable/disable write protect.
Format the Drive, or use regedit to change dword value.
Enable and Disabling of USB write protect using regedit
Enabling USB write protect
[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\StorageDevicePolicies]
“WriteProtect”=dword:00000000
Disabling
[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\StorageDevicePolicies]
“WriteProtect”=dword:00000001