Updater process ended with ERROR: 7

Hallo everyone,
So I wanted to install cyanogenmod on my Galaxy S III i9300, but unfortunately I got stuck and dont know what to do further.
-I installed twrp-3.0.2-1 using Odin3 v3.09
-Downloaded cm-13 nightly and GAPPS
-Wiped everything
-Tried to install cyanogenmod

Reconstructing the log:

Checking for MD5 file ...
Skipping MD5 check: no MD5 file found
symlink: some symlinks failed
Updater process ended with ERROR: 7
Error installing zip file "(directory and name of the zip)

So at this point I tried several TWRP versions and several cyanogenmod version ending up with the same result and getting pretty desperate.

Can anyone help me here?
Thanks in advance

Edit: I of course tried to find a solution without posting first. I saw something about the SD memory formatted as internal memory, but couldnt make a sense of it or how to change it. Also I just bought a micro SD today to do this.
Also I always have to run Odin with the TWRP versions after i got the error since my phone wont return to the menu only to the downloading status with the green android guy