I have exactly the same problem as the poster in question 7864276 except that in my case I've verified that the server is actually running, e.g., from within MySQL Workbench by right-clicking on Local Instance MySQL and selecting Start Command Line Client. It's only when I select Query Database or double click on Local Instance MySQL that the error message results. One additional piece of information in the error message is that it says "invalid for this platform requested(MYSQL_PROTOCOL_SOCKET)". Everything worked fine until I recently updated MySQL Workbench to version 5.2.47 CE.
Click on Manage Connections. Select Local Instance MySQL. Change Connection Method to Local Socket/Pipe. Test connection succeeds now.