I wasn't able to use SD Fix for some reason (just doesn't seem able to edit Platform.XML) but I was able to manually fix it. For those with that problem:
1. In root explorer go to to /system/etc/permissions.
2. Long press platform.xml and then select to open in a text editor
3. Find WRITE_EXTERNAL_STORAGE and add beneath to two permissions:
<group gid=”media_rw” />
4. Save the changes to the file. Now it will work, and I didn't even have to reboot the tablet.