Unknown Error Occurred: Event Log is Full

Problem

You attempt to launch Microsoft SharePoint Designer 2010 and encounter the following errors:

Connection to the WCF service that has connection name {SharePoint site URL} cannot be established.

Unknown Error occurred.  The event log is full.

Solution

Go to the event logs on the machine hosting SharePoint Designer.  Check the Application event log.  Make sure that it is configured to overwrite when full.