As discussed on our blog the process of combining multiple css files will cause problems with css files that make use of @import.
You can go to min/config.php and change $min_serveOptions to true.
The best option, however, is to us CJ Loader to load the file you want instead of using @import.
If you need help, please contact us
PHP Minify requires PHP5.2+ to work correctly, if you are using and older version you should disable CJ Loader. Since many modules come with CJ Loader by default, in case your server uses an older version of PHP you will see the css files on your site not loaded correctky (and leave you with a broken layout). Please go to Admin→Configuration→CJ Loader to disable it.
