Does the adapter have a small sliding mechanism on the left side? One position is for read/write, the other for read only (write protected).
I have this problem with mine too. When I slide it into my laptop's built in card reader it won't go in without sliding the witch to read only. I have to use an external card reader and carefully put it in while making sure the switch doesn't move.
It moves way too easy, probably cheaply made. Your other option would be to use your data cable with the card in the phone and mount to your computer.