Suddenly no data can be written to SD Card from PC (MTP), read Ok, Galaxy Ace 4. What to do? It is not a filesystem error as I tried to install a different SD Card to see if it is possible to copy files to it, same behavior, can read, not write.

There are plenty of free space in SD card. 32 GB total, like 20 or more free.

The problem is reproducible in two operating systems, Windows XP SP3 (Desktop computer), Windows Vista 32 bits (Toshiba Laptop). Right now I don't have access to other systems.

I don't think that this is related to the problem of some apps not being able to write to SD Card. What I'm trying to do is copy files from Windows PC to Samsung Phone SD Card.

In PTP mode Win XP does not even display the content of the SD Card (this is known problem in XP). In MTP mode, It displays it, allows me to copy from phone to PC, but If I try to copy from PC to Phone, the copy stalls indefinitely and no single byte is copied, not even the file created.

In Win XP, Event Viewer shows this message:

Event ID: 15200

MTP USB Driver has cancelled the operation 0x9808


I didn't check Vista Event Viewer yet but I think the same event will appear.

I tried installing Samsung Kies and Samsung Smart Switch, as they install drivers, and then with Windows Explorer again, same situation.

I also Removed Avast from phone and disabled Avast in Win XP. Same result.
This might be a simple problem of a write protection or permissions issue. Take a backup of your SD card and format the SD card. This may reset the permissions and you will be able to write into the SD card