I know this sounds a little weird, but I experienced the same thing using a sd card reader.
I would put the microSD card in its adapter and put it in my 8 in 1 Sandisk reader.... copy the files over.... my phone couldnt read the files.
I bought this: SanDisk MobileMate™ SD™ Plus 5-in-1
My phone can read the files...... there must be something about the microSD adapter that doesnt work well.
my 2 cents