Q:

Using SSH Keys to get access to organizations repository in Sourcetree

I am using github with my own account and I am part of a few organizations. I set up an SSH key to connect to github via sourctree.
So far so good, when I want to add a remote repository I just browse the list of my repos.
Unfortunately I cannot choose from the organizations repositories, where I even added myself as a collaborator, although I have admin rights and even created the repo by myself.
How can I get this to work that I can choose from my organizations repos as well?
(I found a link in another thread pointing to this: https://gist.github.com/jexchan/2351996 but I think that's something slightly different, isn't it?)
Thanks in advance.
Cheers
Edit: I also think that this might be pointing to the right direction: 
unable to get SSH keys working between sourcetree and github
But unfortunately after following @DeepSpace101 's advice I still get the message that 
Permission denied (publickey).
fatal: Could not read from remote repository.

Please make sure you have the correct access rights
and the repository exists.

But I have no idea why I am getting this message.

A:

Alright I got it to work.
The problem was that Sourcetree asked me for the passphrase for my SSH Key. Unfortunately that was not made clear at all. Sourcetrees Interface asked
Password Required
For user **** on host github.com

I assumed that it wanted my password of github. And after entering that I got the message above, that the permission to my publickey was denied.
Only after I tried to clone the repo with my console I was asked for 
Enter passphrase for key '/Users/****/.ssh/id_rsa': 

Which made it clear for me what the problem was.
Well, after a nice struggle I got what I wanted. 

