How do I - Fix the problem where SharePoint Designer 2013 crashes upon opening a site?

This one is REALLY annoying!

I never understood why software vendors always assume that users are on the latest and greatest version of their software.  Furthermore, they assume you're only using the current version by itself.  The REAL WORLD REALITY is much further removed from the utopian vision most vendors have of their products.

In my case, this was a problem back in the previous version cycle, when I upgraded from SharePoint 2007 to 2010.  My clients were migrating from 2007 to 2010 thus having content in both formats.
Of course, this problem didn't go away or get fixed, but instead it persists to this day with the version upgrade from SharePoint 2010 to 2013 and I'll be you dollars to donuts we'll see this problem going from 2013 to 2016 as well.

Synopsis

A large company with multiple terabytes of content decides to upgrade from SharePoint 2010 to 2013.  Given the large amount of data, it's a phased migration over time.  As a result, some sites are in 2010 and some are in 2013.  End user support staff will need to be able to support both 2010 and 2013 sites.  When these users install SharePoint Designer 2013 and then try and open a SharePoint 2013 site with SPD 2013, without uninstalling SPD 2010 i.e. running 2010 and 2013 parallel, then SPD could crash consistently.  Oh, and forget about going back to 2010 also.  It will also now be crashing upon opening a site.  I consider this to be a product bug.
I really wish concurrent version testing would have higher priority with software vendors.

Solution

To solve this little conundrum, we're going to have to hack the system... time to fire up good old REGEDIT.  Follow these steps to clear up the problem.

1. Click the Windows start button.
2. Type "regedit" and press enter.
3. In the registry editor, locate the following key:
   HKEY_CURRENT_USER\Software\Microsoft\Office\14.0\Common\Open Find\Microsoft SharePoint Designer\Settings\Open Site
4. Delete the "ClientGUID" key located here.
5. Locate the next key:
   HKEY_CURRENT_USER\Software\Microsoft\Office\15.0\Common\Open Find\Microsoft SharePoint Designer\Settings\Open Site
6. Delete the "ClientGUID" key here.

Now restart SharePoint Designer and your sites should open as expected.

NOTE:  Your most recently used list will now show both 2010 and 2013 sites.  It's recommended to keep using SPD 2010 with SharePoint 2010 sites and 2013 with 2013 sites.

Hopefully this post saves someone some time and frustration.

Later
C