Do No Evil; Google Chrome Style

Have you seen this warning when you try to click a link in Outlook or Word? "This operation has been canceled due to restrictions in effect on this computer. Please contact your system administrator." Here is a screen shot:



There are many reason this warning can happen. Typically, the cause is that some setting in the registry (the database of configuration data on a Windows computer) has become corrupted. How exactly it became corrupted is an open question. One completely, 100% foolproof, way to corrupt the registry is to install and then uninstall Google Chrome. I discovered this when I realized that the error goes away if you reinstall Google Chrome, even if you do not set Google Chrome to your default browser. It turns out that Google leaves behind pointers to a ChromeHTML file type handler for web pages, but removes the file type handler itself during uninstallation.


To make it easier to repair a computer that has had Chrome installed I decided to write a registry file that restores the registry to its original state, and makes your computer work again. The file ended up being quite long. Google leaves behind a lot of detritus in the registry after uninstalling Chrome. It even leaves behind pointers to file icons in the, now removed, Chrome program.


If you have this error, you can use the registry script below. Or, you can do just the essential surgery by removing these two registry keys:


HKEY_CURRENT_USER\Software\Classes\.htm
HKEY_CURRENT_USER\Software\Classes\.html


That will at least make your computer mostly functional again. To really restore full functionality after you install Google Chrome you need to run the registry file, or reinstall Windows.


Technical Details


When Outlook or Word starts it reads certain registry values to learn which program to use as the file handler for web pages. Those registry keys include HKCR\.htm[l] and the ones listed above. The values in those keys do not actually point to the file handler, but rather, describe the file type of the file handler. Normally, that file type is htmlfile. When you click a link in an e-mail your computer will look up the program that handles the htmlfile file type, and opens the link using that program.


When you install Google Chrome and set it to be the default browser it creates the keys above, along with many others. Those keys set the file type for .htm and .html files to ChromeHTML. The ChromeHTML file type, understandably, points to chrome.exe as the program to invoke. As long as Chrome is set to the default browser the operating system will take the route link->hkcr\software\classes\.html->hkcr\software\classes\ChromeHTML->chrome.exe. If Chrome is not set to the default browser for that user the operating system knows to launch the default browser instead.


When you uninstall Google Chrome it deletes the ChromeHTML key, but not the keys listed above, and many others. When Outlok launches it reads those handlers and tries to find the ChromeHTML file type that those keys defines. The ChromeHTML file type has, however, been deleted. Outlook (or rather Word, which is the email rendering program) catches that but does not have a good error message to show the user. It has been programmed to display the "this file type has been blocked" error when it can't find the file type in the registry. Thus, Outlook and Word (and any other program that handles HTML links)  work correctly when Chrome is installed but not set to default, but fail after you uninstall Chrome and the linkages in the registry are incomplete.


 

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