Почему выходит ошибка при компиляции less в css?

/*Paths to base style*/
@flat-ui-path: "../flat-ui/";
@common-files-path: "../common-files/";
@ui-kit-path: "../ui-kit/";
@img-path: "../../img/";

/*Common styles*/
@import '@{flat-ui-path}less/config.less';
@import '@{flat-ui-path}less/mixins.less';
/*only to flat-ui free*/
@import '@{common-files-path}less/flat-ui-free2.0.0-fix.less';
/* end only for flat-ui free*/
@import '@{common-files-path}less/helper.less';
@import '@{common-files-path}less/mixins.less';
@import '@{common-files-path}less/navbar.less';
@import '@{common-files-path}less/common.less';