It has happened to me, that the switch locked while card was inserted. This is even more true for SD card adapters for uSD card. The switches on my adapters are very easy to move. If I insert the card a bit unevenly, it locks the card 1 in 4 cases, or so...
If the switch is not in locked possition and card seems to be locked, then there might be a problem with the card. Try another one or reformat this one.