You can rescue corrupt memory cards by 'unformatting' them with QA Tool. When you go into the browser after unformatting, the console will ask you to format the memory card as it does out-of-the-box.
So, if you know somebody with a bit spare on their MC, copy your saves to there, unformat your card, reformat using the PS2 browser and copy the saves back across to your card - it'll save you a bit of money in the process too