By default, when the check-in page loads up the Content Type select list automatically sets itself to the first item in the list. Sometimes this can cause problems if users do not pay attention, get lazy, etc. On occasion it will be desirable to force the selection of a Content Type (dDocType). Through the admin server go to general configuration and add this setting:
Restart content server and you should be all set. Now when you visit a check-in page they Content Type will not be preset and users will be forced to make a selection from the list.