There may be a switch on the pen drive to add/remove write protection. Some drives also have a software option of write protection, right click on the pen drive from my computer and you might see 'Removed Write-protection'
For a start, backup the date to your computer in case the drive becomes totally inaccessible.
what model is the flash drive? has happened to me several times and regedit has worked a very few times only unfortunately
side note, wish there was a larger typing space/view when typing alot lol
carrying on, try this Registry Editor method:
Remove your flash drive from the computer
Click Start, in the search box or in Run, type regedit and press OK
You're now in the Regedit window, go to:
If you don't see StorageDevicePolicies then youu'll need to create this folder by Right clicking on the Control folder > New > KeyRight click on Control and click on New > Key. Name this StorageDevicePolicies
Right click on the new folder you just created called StorageDevicePolicies and click New > DWORD Value
Name this WriteProtect
Double cclick on Write Protect and change the Value Data to 0 and then click OK
Close Registry Editor and insert the glash drive back into your commputer ad all should be merry