1. This error happens when the mshtml.dll file is missing or deleted. It can also happen when we repair the registry and damage or delete the mshtml.dll file. To repair this you must install the most current security update for IE7
2. The easiest way to repair this on Vista is to: 1) Click the START button. 2) Click the 'ALL PROGRAMS'. 3) Click 'WINDOWS UPDATE' (in left pane you may need to scroll up or down in Vista depending on how many programs you have installed on your computer. After you click WINDOWS UPDATE, Windows will automatically open the 'SYSTEM and MAINTENANCE-WINDOWS UPDATE' screen. Click on install updates.

3. Another option is to simply click the START button and go to CONTROL PANEL. After clicking on Control Panel, in right pane under the Security title, click 'INSTALL UPDATES.' In the new window, click install updates.
4. For both options you will be prompted to RESTART your computer. You must restart the computer for the updates to install. When your computer restarts, the updates will install. Do not close your computer until they are complete.
5. If you have a different version of IE (Internet Explorer), but have a similar problem you can go to: http://windowsupdate.microsoft.com. The site will recognise your version of IE and your country of origin and guide to the correct version for your browser.
6. If the updates don't work and you have the Vista installation disk, Insert the disk and repair from the installation screen. Click 'Repair', not 'Install'.
7. If you don't have the Vista installation disk: You can do a 'System Restore'. This restores the Windows registry to a prior moment in time (before the registry was changed and caused the problem).
8. System Restore: Start-Control Panel-System and Maintenance-Back up and Restore-Repair Windows using System Restore.
9. If all these fixes fail, you can always find a Free Registry Cleaner. These applications scan the registry for errors and repair them automatically though they may cause some programs to not work properly.