Warning: file_get_contents(/jquery.expander.js): failed to open stream: No such file or directory in _locale_parse_js_file() (line 1488 of /var/www/html/includes/locale.inc).

in case someone get the same error here my tiny solution:

i installed the module (nearly) exactly as recomended in the README
inclusive installation from the Libraries API modue

i cloned the expander librarie from the git hub:
https://github.com/kswedberg/jquery-expander.git

so this path to the expander was
sites/all/libraries/jquery-expander/jquery-expander.js

but this was not working and i got the

Warning: file_get_contents(/jquery.expander.js): failed to open stream: No such file or directory in _locale_parse_js_file() (line 1488 of /var/www/html/includes/locale.inc).

warning

so i figured out that in the
jquery_expander.modudle in line 116
the demanded directory is

  libraries_get_path('jquery.expander') . '/jquery.expander.js' => array('type' => 'file'), 

so i changed the folder name from
sites/all/libraries/jquery-expander
to
sites/all/libraries/jquery.expander

and everything was fine