well my issue is similar and very VERY strange
I have a 2GB microSD card in my phone.
I formatted it with the phone so it would create the folder structure that the phone recognizes
I copied MP3 files to the card.. the phone can read them just fine.
recently I took some photos and videos with the phone and want to transfer them to the PC
I have put the memory card into the same reader adapter I use all the time. it sees the files, in fact, I can read/copy the files from the card that I originally put there with the PC, but I get the access denied error when trying to read the phone created pictures and video files.
explorer says the file format on the card is FAT, so there are no permissions