I can't really help you with the specific problem you are facing, but what I would suggest is that for a live site, not to process the LESS file on the fly with javascript.

Really it should be processed once (either using a browser or some stand alone tool like less.app), with the resultant css copied into a plain css file and linked as normal.
Then you don't have to worry about IE or other browsers not being able to process it.

Alternatively you might want to look at a server side PHP LESS compiler, that caches the output, spitting out normal CSS. -http://leafo.net/lessphp/

Have a look at the less compiler addon (by Korvin). That will process LESS on the server.

If you're using LESS, get it to build into a standard CSS file when you're done editing it.

e.g. if you're using SublimeText2 install the LESS Build plugin:https://github.com/berfarah/LESS-build-sublime... , this will let you work in less syntax, and on save, compiles to CSS.