Cannot modify/delete/create files on SD Card or USB Stick or Thumb drive

If you cannot make changes to your SD Card or Thumb Drive or other flash memory based USB storage, well, then you have problem. But which problem exactly?

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Let’s have a look at some usual causes: 

1. The SD Card is Write-Protected:

a) Some Mini/Micro SD card have a “Lock” switch on the card. The lock switch is typically a tab or switch on the side of the card. Move the switch to the unlocked position. 
Insert the Mini Micro SD card into your electronic device again and check if you can make changes now? If not.. 
b) If you have a Micro/Mini SD card in an SD card adapter, try to get a different adapter. Sometimes the adapter is the problem. 

2. You do not have the right file permissions

a) Maybe you do not have no write permissions granted. Check if your disk file permissions allow you writing  and change them if necessary. But you should get an error message if this is the issue. 
b) b) Maybe the disk is set to be write protected in the registry?

3. The File System of the Storage is corrupted

This can be a bit tricky since there are so many ways for flash memory to go corrupt . First, backup all your data. 
a) Then try the disk check & repair functions of your system. Try chkdsk or fsck. 
b) If there is nothing to repair, try to re-format the storage – preferable with Windows. Make sure to select “default cluster size” and untick “Quick format”. Some people advise to use the SDFormater for this task, but I don’t think this tool is any better than the default disk manager / Windows disk formatter. 
c) You can also try to repartition the disk: Delete the volume via disk manager, create a new volume, quick format. If the disk is still not working… then diskpart command is your best bet here. Some use 3-party partition tools like MiniTool Partition Wizard instead. 
This wikiHow article shows some more approaches. There also are some tools that claim to be able to repair damaged flash drives, but I would not count on them (and always check the tools you download for infections, there are many black sheep’s out there.) 

4. The Storage is dead

If you still cannot make changes to your files, the storage is most likely bad. When SD cards fail, they write protect themselves. You can still read files, but the firmware does not allow writing to prevent further data loss
Move your files to a new disk, dump the old one, and move on. That happens more often than you would think. Plus there are many fake and low quality USB Sticks and SD cards out that break after no time.

Here is some best practice dealing with sd cards & usb sticks from superuser user Tetsujin I’d like to quote:

Golden Rule #1

As soon as an SD card [or USB stick] starts to play up – bin it. They’re not worth the effort once they error.

I go through literally hundreds of them for work. Low write count, high read count.

If they error once, they will error again. Quality control on them is, let’s say‚Ķ variable.

Some of them have a controller chip that will permanently lock them to read only if they detect a write error, as a preservation measure. There is no way to unlock them once this happens.

Golden Rule #2

Don’t use them to store anything valuable.

Note: If the data on an SD card was truly valuable, it is theoretically possible to replace the controller chip, or even directly access the memory itself. This service can be performed by data recovery specialists, but they charge a lot for their efforts & still can make no guarantees.

Rules 1 & 2 are still ‘best practice'”