sd card read error

I had a terrible time getting an SD card to install properly. I struggled for days and days (I know you all know what that is like) and tried different shields, different cards and different software. Finally, I put the card into my Canon Rebel. The Canon tells me "write protect switch is on". Only then do I see the little (very little) switch on the side of the card. That was the problem. I hope this helps someone.