It's probably a lack of enough free space on your Nook OR a problem happened while app was being installed.
Go to your Nook's Settings.
Then click on Device Info.
THere will be two rows there
One of them says 'Space for B&N Content'.
What does that say?
If it's very low, like just 10-20 MB then you have to create free space.
Try the following:
1) Archive some apps that you aren't using which don't save data or game progress.
2) Restart Nook.
Power Off: Press and Hold Power button for 20 seconds.
Power On: Press and hold power button for 4 seconds.
3) Now try to install.
If that doesn't work then get the App Killer app.
Uninstall (i.e. Archive) Bible Tree.
Then go in via App Killer and make sure Bible Tree is actually removed. If not, then uninstall it.
Also check that there are no apps installed that shouldn't be.
Now install BibleTree again.
Thank you for your suggestions. I did actually follow all of those steps before posting here. I appreciate the help though.
I ended up archiving the app and shutting off the Nook for 5 five min. Started it up reinstalled it and it worked. I tried all of that earlier in the day and it had not worked then.
I am assuming it was due to the fact that it was a big update. When I was able to open the app there were lots of updates/changes to things.