Getting an unable to use card message. - Konica Minolta DiMAGE X50 Digital Camera

Try another card, and look for scratches or damage on the gold strips on the card. Check the manual to see which way it goes in the camera.

Try formatting the card with the 'Format' function in the camera menu.
If you read the manual you can can find which card types are supported.

Look at your memory card. SD cards have a slide switch along one edge. The position farthest from the contacts locks the card, protecting it from writes. The position nearest the contacts unlocks the card.

it cannot be in memory card.....

The problem could the SIM card or the phone. Remove the SIM card from the phone, insert it to another phone and try sending messages. If you can send messages then the problem lies in the phone. To verify, insert a different SIM card into your phone and try sending messages. The problem can be resolved by removing the battery and the SIM card from the phone then wait for at least 15 minutes before putting them back.

Usually you just need to reformat the card to fix it. It may be reable in a pc/laptop so you can get anything important off first. Reformat copy your stuff back on and you should be good to go.

And yup this happens rather randomly and at the most annoying time possible usually ;-]

What is the error message?

make sure that the card is not locked on the side. If it is it will not be able to write to it or format it.

Try to slide the little switch on the side of the card in the other direction. That switch is like a write protect for the card. Good Luck.

the card may have become corrupt, try carefully cleaning the contacts with a pencil eraser and try again,or try formatting it using a card reader, but you may have to replace the card.