mobile

I have rooted my S4 mini one week ago, using the CWM recovery. Before that I removed the encryption on external SD card and internal storage.
After root it was sucessful, I installed Greenify (my battery is always so quickly empty), EsDateiExplorer (root explorer), and Titanium Backup. Also I gave Helium superuser access and encrypted both storages again. (Helium didn't work since then)
After getting used to Titanium, today I heard about NAndro Backup, and thought this could be usefull in case I brick my phone.
After having troubles with mounting /data, I read here that it doesn't work with encrypted phones, so I plugged my phone in and waited for 80%. Half a hour ago I started it, and went out of my room, the phone still plugged in.
A few minutes I came back, the screen was still black. It also didn't reacted when you pressed a key. I thought something went wrong and the phone shut down complety, so I pressed the power button for a few secs. Then it booted, but then I got the message that I got to factory reset my device.
I can still reach the recovery and got a backup of all apps on my SD-Card (thank god I did it yesterday). But the SD-Card is also encrypted, and the key will be lost in case I do the factory reset. I can still access the CMW recovery and even can backup the system (just /data is still not working). Does anybody know how to fix it, or safe the SD-Card key?