Wish I had caught the nugget in the above answer that the Xcode bots cannot handle a repository name with spaces.
I had to give up for a while. When Xcode 6.1.1 came out, I tried again, but still struggled for days to get past authentification. Finally located problem when running Xcode manually with logging:
/Applications/Xcode.app/Contents/MacOS/Xcode -XCSUISourceControlLogLevel 2
In the logging, I noticed that someone tried to replace the space with '%2520'. In most other places where the URL to the repository is expanded, one sees '%20'.
I am using a local Xcode server and ssh. So, if your app name has a space in the name (more than a single word), try this:
1) DO NOT USE the "+ Create New Remote..." under Xcode/Source Control/[Your Project]/Configure [Your Project]... (This would create the repository with a space in the name.)
2) Using Server, create a repository without spaces in the name. Select Xcode in the left panel, use the "Repositories" tab, click "+", and type in a name without spaces. Then hit "Create".
3) Back on your development machine use "Add Remote" under Xcode/Source Control/[Your Project]/Configure [Your Project]... (+ under the Remotes Tab). Enter path to the repository like:
Name: origin
Address: ssh://username@servername.local/git/NoSpaceName.git
You may be asked for your password.
When your development machine is able to reach the repository, you can check in code. Then you can go ahead and create the the bot. When creating the bot you may be asked to provide repository credentials. Select change and give username and password. Then select next to set up bot parameters such as Schedule, etc. til bot is created.
FYI. You may be bringing Xcode up and down several times if you need to remove links to old/bad repositories that you will find under Xcode/Preferences.../Accounts and under Xcode/Source Control/[Your Project]/Configure [Your Project]...