How to: Fix Outlook hyperlink error!

I recently came across an incredibly frustrating error within Outlook (in this case 2007, but I know it can affect other versions as well) when a user selected a Mailto (Email) hyperlink within an email. They were presented with the following error:

This operation has been canceled due to restrictions in effect on this computer. Please contact your system administrator.

I went though various attempts at sorting this out. The most popular fix appeared to be resetting the Internet Explorer settings. No joy. Next people blamed default program settings. No joy. Now I was truly stumped. The user said to me that this had only happened since they installed Google Chrome, but they had since uninstalled it. But I could not put anything together!

Now eventually I found a link to a Microsoft FixIt (find it here) which resolves a problem in the Registry. Supposedly caused by the installation/uninstallation of Chrome. Why this isn't affected by default programs or Internet Explorer settings, I cannot work out, but it certainly seems like a good fix for what appears a rather random and "Needle in a haystack" problem.