It will depend on where the card has been used, other than the phone you want to use it in. While SD cards can be moved from device to device, they really aren't meant to. They are easily damaged and different devices can make changes on them causing it to be unusable by another device.
To make it work I would place it back in whatever device you had it in last and clear off the data. Back it up to that device or a computer, etc. Then place the empty card into the phone and it should allow you to mount it and use it in the phone.
In the future when you want to move data onto the SD card from another device to use on the phone, connect the phone via USB to a computer and move the data over to the card while it is still in the phone...