In MicroStation V8 XM versions and V8i 08.11.05.17, if the following key-in is run:
LABEL USEACE [ON|OFF|TOGGLE]The Message Center will display an error
"Unknown key-in or command"
This occurs when the XYZ Text tool is not open
Go to the menu item:
> Tools > Dimensions > XYZ Text > Open as ToolBoxThen run the key-in, otherwise the only option in the Key in browser isLABEL LINEWith the release of the MicroStation V8i (Select Series) versions, this keyin is no longer required.
Instead, select and set the active ACS via the Drawing Scale dialog.
To select the desired ACS click on "Lock Auxiliary Coordinate" button.
Select desired ACS then the Label Coordinates tool will then use whichever ACS is active.
http://communities.bentley.com/communities/other_communities/askinga/w/askinga/label-coordinates-and-auxiliary-coordinate-systems.aspx