...causes serious errors when I try to view a site on older mobile devices.
Symbian S60 v3 and BlackBerry v4.5 cause some serious error so the rest of the stylesheet won't execute (it looks as though stylesheets are turned off). When I remove the normalize.css code everything works again.
The mobile version numbers (or anything mobile related) don't really matter. The question is: is there anything in the normalise.css that could look like it could break anything. I mean setting a width on an element isn't going to, so it must be some new modern command or something.
Normalize.css is a huge reset file (Nicholas Gallagher and the other developers write convincingly that it's more than "just a reset," but let's just use the term....) Anyway, big honking resets often wreak havoc when they are used in displays. Normalize.css is an HTML5 reset -- some older mobile platforms might not handle HTML 5 very well. Your best bet is to try it as it stands in a broken device, then remove (and replace) one chunk at a time until you find which element of the reset is breaking the display. When you identify it, then you can decide whether it's worth keeping or not. Resets ALWAYS need to be configured for specific uses.