Are you using the Acer Sync program from their support.acer.com website? Even then, I do not think that it is designed to work that way and is more to sync the data on the tablet itself and not the "external SD card". My only suggestion is to take the micro-SD card out and put it in your PC to get the data off.
*Edit - You can also sync your contacts, calendar, and camera pictures using the Acer Sync, not just files.