I’m still in the stage of migrating to SharePoint 2013. As a preparatory step, I uninstalled SPD 2010 and installed SPD2013 as SharePoint 2013 requires SPD 2013. At some point in the migration, I had to update a SPD2010 workflow. Guess what? SPD2013 isn’t compatible with SharePoint 2010. So I reinstalled SPD 2010 but every time I click the Open Site button, it crashes.
Luckily, I still had the Recent Sites list so I could still use the tool, I just had to start at the root site and navigate my way down. After a month of “dealing with it”, I asked Google for an answer. Luckily, someone else already went through the tough work of diagnosing the problem and offering a solution. His case is the reverse of mine (he probably didn’t uninstall SPD2010 first) but the resolution is the same.
Delete the ClientGUID keys (both of them) to resolve the issue.
Here you go: http://sympmarc.com/2013/04/16/sharepoint-designer-2013-crashing-on-open-site-the-fix/
Adventures of an Oregon K12 IT Director 