This card formats fine. (Both on my PSP and through Windows)

This card reads fine, anything I manage to put on it I can see when I access it. I can move files around and create new folders. I can rename files. I cannot however unpack anything on the card. Unraring anything gives me an error saying the memory stick doesn't have enough space (when it has nothing on it of course).

I can transfer files under about 200 kbs to the card fine. Anything over that and it gives me an error message saying the following: "Cannot copy (whatever): cannot find the specified file. Make sure you specify the correct path and file name." Or it just closes the window and says nothing. I've tried using the memory stick both through a card reader and the PSP. Same thing happens on both.

Here's the thing. If I put it in my PS3 and transfer things (much larger than 200 kbs) to it, it has no trouble at all. I ripped a CD on the PS3 and transferred 40 mbs worth of stuff to the card and it worked fine. Downloaded things off the internet through the PS3 browser and it worked fine.

So what's the deal? Is it the memory card or my computer? And what...if anything...can I do? (Other than trying to send it back.)

I don't have another computer readily available that I can test it out on.

Any help at all would be appreciated. If you need any extra info let me know. I am running XP.

Alright, so I sent back the memory stick thinking it was defective in some way. While I am waiting for another to shipped back to me I went and bought a 1GB SanDisk Pro Duo card. And lo and behold it is doing the exact same thing as my 4GB card. So needless to say when I get my replacement 4GB card it will inevitably be just as messed up.

What in the world could be the problem here?

I've tried four different card readers on six different PCs. The only thing similar between the computers is that they are all running Windows XP. Which isn't the problem of course.

I really can't be so unlucky to run into a continuous batch of corrupted memory cards can I?