Seems like this could be my problem, too. But the link (http://www.episerver.com/templates/page.aspx?id=3802&epslanguage=EN) is dead. What document did it point to?
The problem showed itself in EPiServer CMS 4 in the way that you got an error when you tried to download a versioned file larger than ~60k. The problem was a Windows 2003 SP1 problem. The relevant Microsoft kb-article seems to still be in place:
If you need further information I'd suggest you contact our support department. I haven't encountered the problem in quite some time and this is pretty much all I can remember :)
Per GunsarfsEPiServer CMS Development Team