Why does my card do this?

Why does my card do this? It's a decent card, 15 mb/s, 4gigs, but 50% of all the pictures I stick on my computer comes out looking like this; broken up and discolored.

I have to copy them over several times for them to come out normal. They're written correctly on the card, but they just don't transfer correctly off of the card.

 

Try to reformat the card, it could be corrupt somehow.

 

I reformat it every time I transfer a days worth of photos to my computer.. it's more healthy for the card, but it writes them correctly when I transfer them a few at a time...