I've had a problem signing in to iTMS with my account because my ethernet adapter wasn't named "en0", but "en2". Because of this, iTunes was throwing me an error, saying that it cannot log me in, and returned an error id of -50.


The solution is really simple. First, check which "enX" are you using (which is active and working), then open up terminal, and type in this:

Enter your password, and then edit the file. Search for your "enX" in it. The part you want to search looks like this:

The X in the code above represents the number you have for your active connection. Change "enX" to "en0", and "X" to "0", so your code should look like this:

After this, scroll to the beginning of the document, and search for "en0" - the first in the list, then edit that, replacing the 0 with the number your connection had. Also don't forget to edit the <integer> part too, so in the file there won't be two <integer>0</integer> lines.
Then press CTRL-O (save), Enter, then exit. Restart the system.
Be sure that after the restart, you add your newly renamed ethernet to the network list, because without it, your old - and modified - "enX" network adapter tries to connect to the internet.
And that's all, iTMS works.

I hope this was helpful to you all who bumped into this problem.