My micro SD card doesn't allow me to add anything to it

Every time I try to add something it says

the disk is write protected

remove the write protection or use another disk

I don’t know what’s  wrong with it it is not locked or anything like that those any one know how to remove the write protected thing?

What size is the card? Could be the SDHC format (4GB and up) isn’t recognized. These players pre-dated this larger format and can only read SD (2GB and under).