This is usually caused by the SD card adapter, and is nothing to do with the camera or the microSD card. On the SD card adaptor there is a small slider - which allows you to lock the card (to prevent accidental erasure).

If you put in on the table with contacts upwards, corner cut top left, then the slider is on the right hand edge, about 1/3 the way down. If it is slid to the top position (nearest the contacts) the card is unlocked. If it is slid down (away from the contacts) the card is locked. (In the above picture, we are talking the left adaptor, and the left hand side - just where the line splits the red from blue).

If it is a damaged / "cheap" adaptor card, sometimes the slider falls out, in which case the card is locked. You can still read from it, but not write to it until fixed or replaced.

First check is to move the slider to locked, then back to unlocked. The replace in the MMC reader and see what you get.