it can be any of the following scenarios
There is a write-protection tab on the mini sd card HOLDER. Every time you insert this into your PC or card holder, this tab slides to the write protect position. Either keep resetting, inserting & reinserting until it doesn't slide or tape it down.
There is nothing wrong with the mini sd card. Simply locate the write protection key and push it.
The mini sd card has some error: Go for a low level formatting.
The card has virus: Remove the virus.