I've recently encountered the same sort of problems when attempting to transfer files from the pc to the phone. It had been working fine for several months and the starting flaking out the past couple of weeks. Sometimes Windows will recognize the phone's SD card, the file transfer will start and the abend with a Windows error. Other times, the pc won't recognize the SD card at all. USB debugging is not selected and I've got the USB cable connected into a powered USB port on the pc. I'll have to try it out on a different pc to see if that makes any difference (and to see if it's a Windows issue). In the interim, I'll probably get a card reader/writer for the Micro SD card.

I've done everything listed here. I've done with and without USB debugging (also with and without mock locations and screen never timeout and every combination thereof); without drivers; with drivers; with repaired drivers; uninstalled drivers; rebooted phone and computer; reinstalled drivers; re-rebooted; re-uninstalled drivers; re-rebooted; installed different drivers; got dizzy; drank some water; took a nap; grew a beard; used every single hub on the computer 30+ times (each); tried 5 different cords; called customer support 3 times; used my inside voice and said please and thank you; tried the sd card in an external sd adapter; crossed my fingers; toes, eyes, and alter-egos; did 100 hail marys; danced a raindance; spun around in circles clockwise 33 times; fell down; begged for death to take me; ate a jelly bean i found under the couch, got up, barfed, fell down again, got back up again, gnawed off my own eyebrows; beat mortal kombat on expert setting with each and every character in the roster; ate all 5 cords; buried my Epic in a hole in the front yard; waited 7 blue moons; dug it back up; dropped it in a bag of white rice; microwaved it; waited 3 days, and ate it. My stomach kinda hurts.
Any suggestions?