How to reproduce:

1. Open xfce4-panel-profiles;
2. Click 'Import' button;
3. Now the file chooser will be opened, select any invalid configuration file and click 'Open';
4. Now a dialog will ask you to specify a name for this configuration, click 'Save Configuration';
5. The UI will freeze.

Traceback:

Traceback (most recent call last):
  File "/usr/share/xfce4-panel-profiles/xfce4-panel-profiles/xfce4-panel-profiles.py", line 255, in on_import_clicked
    self._copy(filename, dst)
  File "/usr/share/xfce4-panel-profiles/xfce4-panel-profiles/xfce4-panel-profiles.py", line 93, in _copy
    PanelConfig.from_file(src).to_file(dst)
  File "/usr/share/xfce4-panel-profiles/xfce4-panel-profiles/panelconfig.py", line 76, in from_file
    pc.source = tarfile.open(filename, mode='r')
  File "/usr/lib64/python3.7/tarfile.py", line 1578, in open
    raise ReadError("file could not be opened successfully")
tarfile.ReadError: file could not be opened successfully

Proposed solution: add an alert dialog and go back to main window.

I'll try to fix this bug in the next days.