Hi everywhere, firstly thanks for the great solutions in the thread though I'm sorry to say they did not work. I was about to try my final option of creating a folder with TB on the internal memory. I am running cm13 for the nook HD +. Anyway think I may have found an alternative solution... I also found that the setting in SuperSU didn't make any difference.
Go to Preferences, backup folder location. At the top it says Storage provider, click to change and I selected Document Provider. The middle one for android 5.0+ then select the backup folder on your sdcard. I the reloaded the application from TB. Now all is fixed. It occoutred to me due to having to manually allow apps like solid explorer to access it in this manner.
I suggest you try this solution first as it just so simple, can't believe it wasn't in the thread (or maybe I just missed it)
If this helps please hits thanks
Thanks again for all the info n solutions I tried tho