internetexplorer.application and explorer.exe problem

Hi all,
I have a problem on one of my PC (windows XP SP3, IE7, all patchs done)

When the system open an "internetexplorer.application" OLE object
(in windows live messenger, the option for accessing to the mails for example)
it is c:\windows\explorer.exe which is called and not
c:\program files\internet explorer\iexplore.exe

This cause me a lot of problems with some others applications who expect
iexplore.exe and not explorer.exe

Someone can help me to corrige this ?

Sorry for my poor english :-)
--
Sincerely Yours
Themis