In your Vista, if your Internet Explorer gives you any one of the following error messages In Windows Vista, even after you log in with an administrators account;

then you may have to download and install this hotfix.
Update for Windows Vista 32-bit version
Update for Windows Vista for 64-bit version

This problem occurs if you try to start Internet Explorer 7 on a desktop that is not the default desktop. A program may switch the user to a desktop that is not the default desktop. This problem occurs because some security enhancements in Windows Vista prevent the user from starting Internet Explorer on a desktop that is not the default desktop. More at KB935855.