Undefined mixin 'zen-grid-item'

I am stuck on this and can't compile my sass. I have zen-grids gem installed.
I get this error when i run "compass compile": "Undefined mixin 'zen-grid-item'" Does anyone have any idea what i should or not be doing?

.aside1 {
 @include zen-grid-item(2, 1); // Make this grid item span 2 columns.
position: relative;
left: 34%;
}
.aside2 {
 @include zen-grid-item(4, 4); // Make this grid item span 4 columns.
}

error sass/responsive.desktop.scss (Line 16: Undefined mixin 'zen-grid-item'
.)
Sass::SyntaxError on line ["16"] of /mypath/sites/all/the
mes/vip/sass/responsive.desktop.scss: Undefined mixin 'zen-grid-item'.
Run with --trace to see the full backtrace