susy-compass - Susy：语法错误：未定义的操作：“1/0.623em 乘以 1em”

Question

尝试将 susy 与 middlemanapp 一起使用并在基本设置后出现以下错误

Syntax error: Undefined operation: "1/0.623em times 1em"
        on line 32 of .... /gems/compass-0.12.2/frameworks/compass/stylesheets/compass/typography/_vertical_rhythm.scss
        etc.
        etc.

信息：

gem "middleman", "~>3.0.7"
gem "susy", "~> 1.0.5"

$ ruby -v ====> ruby 1.9.3p194 (2012-04-20 revision 35410) [x86_64-darwin11.4.0]

_grid.scss

@import "susy";

$total-columns  : 12;
$column-width   : 60px;
$gutter-width   : 20px;
$grid-padding   : $gutter-width;


.container { @include container; }