Using Server-Side filters requires defined prompts with default values in Information Map Studio. But it is extremely important to note that changes to the default values (or adding a default value) to the map while the related dashboard is in use can cause some issues.

The documentation has this noted in red bold CAUTION text. So it is really important.
"Do not change the default value of a prompt in another application while SAS BI Dashboard is running.
Log off from SAS BI Dashboard, change the value, and then log in again."

To avoid these, simply log off the BI Dashboard application. And if it's too late, or if you can't get all the dashboard users to log off, a restart of the web application tier (JBoss, WebSphere) will do the trick.