ICalculator is a Desktop interface. It is not installed by the Engine product. This is the case with any interface or class that is part of an ArcObjects library whose name ends with UI.
The reason for the error is clear - you're trying to use a Desktop-only interface in an Engine application. If the only thing you have installed on the target machine is the Engine runtime then that interface is not there because Engine doesn't install it.
Is your Engine application binding to the Desktop product and checking out a Desktop license?
You're binding call is set to Engine or Desktop. Try changing that to Desktop only. The way you have it now it could be binding to the Engine product, which doesn't include the interface you're trying to use.