TypeInitializationException: "System.Array.Empty" when opening Forecast 5

TypeInitializationException: "System.Array.Empty" when opening Forecast 5

Issue:

After an upgrade, you are receiving the following error when opening Forecast 5:

TypeInitializationException
The type initializer for 'Forecast5.Model.Node' threw an exception.
TargetInvocationException
Exception has been thrown by the target of an invocation.
MissingMethodException
Method not found: '!!0[] System.Array.Empty()'.
   at Forecast5.Model.Node.set_NodeType(NodeType value)



Cause:
The .NET Framework has not been upgraded correctly.

Solution:
Install on the PC you are receiving the error.
Restart the PC/Server.
Forecast 5 should now run successfully.