//RWT-OEI 12/08/05
//This function allows the script to display a GUI on the player's client.
//The first parameter is the object ID owned by the player you wish to
//display the GUI on.
//The second parameter is the name of the GUI screen to display. Note
//that only screens located in the [GuiScreen] section of ingamegui.ini
//will be accessible.
//The 3rd parameter indicates if the displayed GUI should be modal when
//it pops up.
//RWT-OEI 01/16/07 - Added 4th parameter. This defines the resource
//that should be used for this screen if the screenName is not already
//found in the ingamegui.ini or pregamegui.ini.  If left blank, then no
//gui will be loaded if the ScreenName doesn't already exist. If the
//sScreenName is *already* in use, then the 4th parameter will be ignored.
void DisplayGuiScreen( object oPlayer, string sScreenName, int bModal, string sFileName = "", int bOverrideOptions = FALSE);

The description supplied by the toolset is in error. GUI scenes must be listed in the [MandatoryGUI] section of ingamegui.ini. Further, "All GUI screens which can be invoked by script must have the scriptloadable=true setting in their main root node." ( 34 )