I tried all the tricks I could think, formatting with FAT instead of FAT32, format in computer first, with no luck. Sadly, you may have to use 2G cards in your D50. All my 4G SD cards are the newer SDHC (high capacity) ones not the older SDSC (standard), you may want to try and find some of the older SD or SDSC cards. Some older SD cards were made over the official 2G limit of the SDSC specs before the newer SDHC specs were introduced, no guarantees they will work in the D50 as they are not officially supported. I have several 2G cards that all work with my D50, but I cannot locate any of the older 4G cards to see if they would work too. The good news is that the older cards are cheap, well until it gets known that they are the only cards that work in the older cameras.... hmmm... I'll heading to the dollar store, see if I can get them at 2 for a buck.
Will shoot for fame...fun...food... a heck I'll shoot anytime anywhere.