When editing a script stage in a workflow and using a function built in another global module, such as NonInteractiveProcessor, the error appears:
The type or namespace 'MyNamespace' could not be found (are you missing a using directive or an assembly reference?)
public class Math
public static int multiply (int n1, int n2)
var n1 = 1;
var n2 = 2;
int result = MyNamespace.Math.multiply(n1, n2);
When modifying the script, the Namespace ("MyNamespace" in this case) was not saved correctly on the Project level.
Apply to save all the changes done to the script and the project in general (the Apply button should be grayed out).