Although it is not recommended to use SQL server 2008 R2 express as a Certify database especially for production system, sometimes to train users or to test a new functionality of a new release of Certify - one may choose to install Certify database on a SQL server 2008 R2 express.
Please note that if the default instance is used to install SQL server 2008 R2 express, the full servername must be used (instead of localhost).
For example, if the machine name is xyzserver then, please enter xyzserver (not localhost) into the Change configuration dialog. Entering localhost will seem to work as the "Test database" button will say that the setting is valid. However, when starting up Certify, the user will get the error message that the database (localhost) does not exist. When this happens, please go the Change configuration dialog and enter "xyzserver" as the database server.