Hello,
One of my users was getting "Invalid HTTP Request" errors when doing uploads to a photo album package using IE 6 on winXP. Dirk Gomez on #openacs suggested increasing the "socktimeout" parameter in the nssock configuration section. (not the "timeout" parameter listed in the sample configuration file.) Increasing that timeout value from the default 30 seconds to something larger (I used 240 seconds) made the Invalid HTTP Request error go away. This is with AOLserver 3.5.1.
Figured I'd post here in case someone else trips up on this.