I deleted a folder on the memory card Optio S50

Help me please tekkies!

I have a 1 gig SD memory card that I put into a card reader on my Mac and then after I transfered the files from the card onto my computer, I deleted them by dragging this folder with them into the trash. Originally, the card only had one folder that automatically popped up. After using it for a while there were more folders that would appear. I usually just threw the whole folder away no problem. This time, way after I transfered them and removed the memory card reader, I noticed there was something stuck in the trash can. I tried to move it back to the desktop after it would not just delete permanently, and it would not go. I then attempted a few more times, then finally it asked me to put in my Admin password and so I did, and it successfully disappeared.

Now, it reads "Memory Card Error". I figured oh well, I'll just buy a new Memory Card and thought since I deleted that folder the card was kaput. So I got a 2 gig SD and put that in the camera, to only find the same error message. I feel like I have to junk this thing now although it works and still takes pictures. Is there any way I can fix this? Like re-typing a certain set of numbers for the folder that was discarded? They had a series of numbers and some letters, so I don't know... This one seems tricky to me.

Thanks!