Never had a problem like this before. Could it be the card reader and/or SD disk is bad?
You mean: no problems with the same SD card in the same hookup with card reader and Mac?
Of course card and/or reader could be bad*, but the trick is in isolating the culprit. For example, does the problem also occur on another computer, and/or with another card reader (assuming you've got access to one)?
*) If things are working, however slowly, it's not likely a hardware problem, which tends to be an all-or-none phenomenon.