Why is there an error when compiling less to css?

Question

css

Startup Design Framework_v1.1.3 when compiling this code, an error occurs, the compiler uses WinLess
Here is the code:

/*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';

This is the error that comes out: