You could open up the memory card to make sure there isn't any excess dust and that nothing is loose.
Be careful as static could damage the memory card so don't touch the components.
You could also give the contacts a light clean with a cotton bud to remove any excess grease etc that may have built up on them.
Unless you have a save that you dont really want to lose, buy a new one.
You can pick up a non sony 64 MB card pretty cheap on ebay. I picked up a 64 MB magicgate a year ago and have had no problems.
Either way, you will need a new card now, so just hope you can transfer the saves from old card.