Admin styles not loading css, admin_enqueue_scripts

I have a small plugin that basically changes look of admin side menu.
I used it on single WP install and would like to use it on our new MU install to change all wp dashboards.

I uploaded plugin and Network enabled it but css files are not loading correctly.
Looking at source code of the subsite it loads up but clicking on the css file link it does not load file.
This is content of it in source:

<title>500 Internal Server Error</title>
</head><body>
<h1>Internal Server Error</h1>
<p>The server encountered an internal error or
misconfiguration and was unable to complete
your request.</p>

Link points to wp-content/plugins/adminstyles/css/ow_styles_adminbar.css

In plugin I use:
add_action( 'admin_enqueue_scripts', 'ow_admin_theme_style' );

Is there a different way to load css in MU other than "admin_enqueue_scripts"

Thank you.