方法1：In the solution property page, check the platform of the assembly that contains "UpdatingMediaElement" and the assmeblies that contain any of the superclasses and interfaces from which "UpdatingMediaElement" subclasses or implements. It appears that the platform of all these assemblies must be "AnyCPU".
方法2：
Try to do these:
In VS, right click on your Solution -> Properties -> Configuration Properties
A new dialog is opened, try to change the project configurations from Debug to Release or vice versa.
After that, re-build your solution. It can solve your problem.