Trying to transfer data to SD

When the notification comes up that I'm 75% full it offers me to transfer all data to the SD card. I've tried several times to move all the app data possible to the SD card (as I have about 20gb free on it) but it gets stuck on about 6% I've left this for a day but still gets no further. Any way of sorting this out? I'd like to just free up some of the internal memory space. Everything else on the tablet is on the SD card, so just apps remain.

Thanks