IE6 Blank Subject Line Fix
Microsoft has released an update (thankfully) that fixes this problem.
http://www.microsoft.com/windows/ie/download
/preview/ie6/ie6update.asp
This is what you had to do before the fix was available (saved for posterity's sake)
Replace the version of mlang.dll installed by IE6 with the version provided with your last copy of Internet Explorer.
Search ...\windows update setup files for files *containing text* mlang.dll - leave the file name area blank. This will show you what cabinet file contains the file in question - point System File Checker to that folder. The restore location is ...\windows\system.
Mlang.dll could be in any of these *.cab files
iemil_2.cab
iew2k_1.cab
ient_3.cab
ie_3.cab
Note: The IE6 public preview has been refreshed and is now V.2479. It is recommended that you download and install this refresh (after uninstalling the old beta). It contains several bug fixes and the cookie options are much more complete.