Unable to check Email and getting MSN.Mailhost error within MSN Explorer
I was working on a system and everything was working except for the fact that when using MSN the Email was not working. It would show the count of how many new messages were in the Inbox but when you selected the Mail button I got a "cannot open this file" error message for msn3.mailhost. I went to re-install MSN but then I got the message that all components were already installed. This system was also running McAfee Internet Security along with Windows Defender but I couldn't find any settings that looked out of the norm for either program. I finally stumbled across this solution and it worked!
The Regsvr32 command-line tool registers .dll files as command components in the registry.
Click "Start" and then "Run" and type in
regsvr32 c:\progra~1\msn\msncorefiles\mailui.dll
(updated 05-23-2007)
Downloadhost error message within MSN Explorer
The problem and solution are similar to the above. Open the Run dialog as above but for DOWNLOADHOST type the following:
regsvr32 c:\progra~1\msn\msncorefiles\msnmetal.dll
This re-registers the msnmetal.dll file and should solve the problem. If you are signed into MSN, sign out and then sign back in and everything should work OK (though, some reports are that the error still pops up even though the downloading will work - this may not be all that is needed).
found at http://www.cknow.com/faqs/Why/HavingaMSNMAILHOSTDOWNLOA.html
(updated 08/06/2007)