There is more than one B0 block inside the DB.
There is more than one root block (B0). All programmatic design decisions were based on having only one root block (B0).
This error could be caused by several users entering Planning at nearly the same time, when the B0 block had not yet been created.
This situation could cause the loss of ability to interact with some objects in the database through the assembly hierarchy.
What You Should Do
A database integrity repair SQL script or COM tool has been provided to correct this problem.
Open the model.
Run the Clean Database custom command.
Select the object in the list of objects.
Click Clean Now to repair the object.