Running clone.sh when you have no github account or no special permission results in the following command being executed:
$ git clone git@github.com:RangeNetworks/asterisk.git
Cloning into 'asterisk'...
Permission denied (publickey).
fatal: Could not read from remote repository.
Please make sure you have the correct access rights
and the repository exists.
The solution could be change the script to clone over HTTP. Alternatively the permissions of the repositories could be changed.