Error message in WF4: "Error: The values provided for the root activity's arguments did not satisfy the root activity's requirements"

When loading an activity assembly using Assembly.LoadFrom, you may see the following error:

"Error: The values provided for the root activity's arguments did not satisfy the root activity's requirements: 'UserDefinedInputClass': Expected an input parameter value of type 'MyAssembly.UserDefinedClass' for parameter named 'UDC'. Parameter name: rootArgumentValues"

Assembly.LoadFrom does not use the main application context; instead, a new context is used, so type checking fails with the above error.