The file extension Downloadhost is associated with MSN and when you get DOWNLOADHOST or MAILHOST problem messages, chances are, the DLL files have become unregistered and so users cannot log in to their MSN account. This is usually caused by registry problems or when some registry cleaning programs inadvertently deletes the MSN DLL files.

To fix this problem you need to re-register the file extension Downloadhost. If you're getting the MAILHOST problem message, go to Start -> RUN and type this on the dialog box: regsvr32 c:\progra~1\msn\msncorefiles\mailui.dll

If you're having the file extension Downloadhost problem, the solution is almost the same, you just have to type this on the RUN dialog box: regsvr32 c:\progra~1\msn\msncorefiles\msnmetal.dll

Sign-out of MSN and sign-in again. If the problem still persists, you many need to contact MSN Support.