When trying to connect and when working with the Object Explorer. Toad seems to hang for a moment, and then gives an "end program" dialog or "root element is missing" error.
Corrupted files in settings.
Go to C:\users\<personal folder>\AppData\roaming\Quest Software\Toad for Data Analysis <version> and rename the full directory.
Open Toad and test the issue. This will force Toad to recreate the settings directory with default values. This will also remove Toad configurations and history.
Go to C:\Users\<personal>\AppData\Local\Quest Software\Toad Common Files\Object Annotation Cache (by default) and rename the "Quest.PersistentCache.xml" file.
Open Toad and test the issue. This is will force Toad to recreate that file.
The setting under Tools | Options | Database | Cache | "Object Annotation Cache" specifies the directory of this file, whether it's a private file or shared.
Uninstall/reinstall Toad using the Quest Installer.