Free space on SD memory card

[DonKiddick]

I have a 512MB SD card on which I store .jpg pictures transferred from my hard drive or from emails. When the card is less than 20 percent full - 81MB used, 430MB free - I get an error message saying that I can't store any more pictures. If I delete a couple of pictures I can then add a couple more before I get the error message again. The 81MB used comprises approximately 200 photos with no individual one bigger than 1MB. Is there a limit to the number of photos I can store, irrespective of MB used or have I got a faulty card? I asked this question of the card supplier but they didn't give me a satisfactory answer - they just sent me a new card which behaves in exactly the same way.

[puzzlesRus]

Just for the hell of it, why not try saving a single file of, say, 450MB to the card and see what happens. Any file will do, data, video etc.

[rojash]

It may be that the filing system can't deal with so many files in a single folder. Try creating a new folder for each batch of pictures.

[heathfield]

I may be stating the obvious, but have you tried reformatting the card in the camera? The card format can become corrupted, and this can produce the symptoms you're experiencing.

[DonKiddick]

Thanks for your answers so far. I should point out that I don't use the card in my camera. I use it to load photos from my hard drive or from emails so that I can view these om my Philips Digital Photo Frame. This DPF doesn't read cards from my camera - which is an Olympus mu 400 that uses xD cards. Also, it's a quirk of the DPF that it will only read from the root directory of a memory card so I can't keep pictures on the card in different folders. Similarly, my computer is a bit long in the tooth and I only have Win 98SE. I know that there is an obvious answer to upgrade my PC and or my camera but I don't want to do that!
I would like you to share any thoughts you might have about the liklihood of my cheap and cheerful SD card being faulty. I know I could by another card and try that but you'll probably gather from the above comments that I'm a bit of a cheapskate. Thanks!