Cannot call method 'charAt' of undefined in sprites.less

Created by: iriscoopers

Hello,

I've just downloaded the new update and I'm using less.1.2.1. Set up a simple test page using the fluid.html example but I get the Cannot call method 'charAt' of undefined in sprites.less error. (on my local server)

If I comment out @import "sprites.less"; in bootstrap.less it works fine.

The urls to the img folder are set correctly in variables.less so i'm kinda lost. Quite new to less too. I'm compiling it on client side.

Any advice is much appreciated, thanks!

Iris