Error message: "You cannot Detach a model from a managed model. The operation is cancelled."
Unable to detach some Reference Files in MicroStation 08.11.09.714
Verify if this MicroStation version is used as prerequisites for Inroads, Mx, GEOPAK 08.11.09.845+. This MicroStation version is not a Standalone version.
This reference files likely have dependencies in a Civil model. If a user detached one of these references they could permanently break relationships in the element rules.
Beginning in InRoads / MX / Geopak version 08.11.09.845 this safeguard was added. If you attempt to detach a reference in MicroStation (without InRoads / MX / Geopak loaded), you will be unable to do so and will receive the above message. This is due to the fact the references likely have dependencies in the current civil model. If a user detached one of these references, (s)he could permanently break relationships in the element rules.
In order to detach these references, open the DGN file with InRoads/GEOPAK/MX running inside of MicroStation. In the process of detaching the reference you will receive the message below. Selecting "Yes" will detach the reference, but may potentially break the relationships between elements. Selecting "No" will cancel the operation.
Original article in Roads and Site Design communities:Unable to detach reference in MicroStation