After certain changes in the admin, it might be necessary to clear the server cache to apply your settings. This applies mostly to the user permission and multi-subdomain settings.
If you use more than 1 admin, it's you need to refresh cache on ALL of them!
That is NOT your browser-cache - it is cache of data stored on the web-server, that avoids unnecessary calls to the database by "storing" commonly used (but NOT commonly changed) data.
Cache reloads automatically every 10 minutes