gpg: keybox '/tmp/tmphgbhzf6a/pubring.gpg' created
gpg: /tmp/tmphgbhzf6a/trustdb.gpg: trustdb created
gpg: key F1773AF13B1510FD: public key "Launchpad PPA for GNOME3 Team" imported
gpg: no ultimately trusted keys found
gpg: Total number processed: 1
gpg: imported: 1
gpg: no valid OpenPGP data found.
Exception in thread Thread-1:
Traceback (most recent call last):
File "/usr/lib/python3.5/threading.py", line 914, in _bootstrap_inner
self.run()
File "/usr/lib/python3.5/threading.py", line 862, in run
self._target(*self._args, **self._kwargs)
File "/usr/lib/python3/dist-packages/softwareproperties/SoftwareProperties.py", line 688, in addkey_func
func(**kwargs)
File "/usr/lib/python3/dist-packages/softwareproperties/ppa.py", line 386, in add_key
return apsk.add_ppa_signing_key()
File "/usr/lib/python3/dist-packages/softwareproperties/ppa.py", line 273, in add_ppa_signing_key
cleanup(tmp_keyring_dir)
File "/usr/lib/python3/dist-packages/softwareproperties/ppa.py", line 234, in cleanup
shutil.rmtree(tmp_keyring_dir)
File "/usr/lib/python3.5/shutil.py", line 480, in rmtree
_rmtree_safe_fd(fd, path, onerror)
File "/usr/lib/python3.5/shutil.py", line 438, in _rmtree_safe_fd
onerror(os.unlink, fullname, sys.exc_info())
File "/usr/lib/python3.5/shutil.py", line 436, in _rmtree_safe_fd
os.unlink(name, dir_fd=topfd)
FileNotFoundError: [Errno 2] No such file or directory: 'S.gpg-agent.extra'

Welcome to LQ, but read the FAQ about info to include when "Asking questions".
Maybe this?: http://forum.librepilot.org/index.php?topic=2755.0

Web-searching is often most effective; I found that from the top Traceback line.

Your question tell us nothing other than the fact you have a "problem adding a repository", which is useless in us being able to provide much help.

See this: https://www.linuxquestions.org/quest...#faq_lqwelcome

lekhan, which distro? which repository?
you clearly added a "ppa for gnome3" - why would you need that on ubuntu?
and if it's not ubuntu or one of its derivates, you shouldn't use ppa's!