I had the same problem; The reason is that the sdcard was not set to size.
By opening the "Android Virtual Device Manager" and editing the device, I can change the size of the SD card, or at least make sure that it is not blanc (since this was my problem). After saving the changes and rebooting the emulator, and in my case alse Eclipse, the read / write permissions were set correctly, and I could add files to the SD card in the emulator.
source share