I think that you're getting parsing errors and no output because PDF::FromHTML doesn't "utilise CSS"---it won't convert CSS and wasn't designed for CSS. Check the CAVEATS section, line 205 in FromHTML.pm for more info. I ran html2pdf.pl on 10 files and got nothing back. All of my HTML files have CSS in there. I'd dump PDF::FromHTML and use HTML::HTMLDoc.

update: HTML::HTMLDoc uses HTMLDOC. HTMLDOC 1.8.x doesn't support CSS; however, 1.9.x supports CSS1 and CSS2.