Hi,

This is due to a bizarre limitation of IE - it'll only import so many stylesheets and then refuses to import any more. Not sure what Microsoft's reasoning is for that. It often happens when there's a lot of modules enabled that each import their own CSS. You can solve it by navigating to Administer > Site Config > Performance and enable the CSS optimizing, which will combine all the CSS. It will also cache the CSS, so if you're make changes to the stylesheet you'll have to clear the cache to see the results.

Another reason to hate Internet Explorer. I'm not really sure what the software "engineers" at Microsoft do all day, but "create great software" isn't one of them. It's the only browser with this limitation, which means there's a way to eliminate it, but I'll wait for IE 12 to get that done. :/

Thanks, Rob. I've just turned on CSS caching and it solved the issue. I assume that turning it off again will require me to clear the caches if/when I make changes to the stylesheet and want to see them immediately. Do you know if that is correct?

Yes, that's correct. If you're doing any changes to the stylesheet you'll want to disable the caching. I've forgotten on occasion and ended up bewildered when nothing updates. hehe.