If the Viewer won't start maximized when the runtime is started and 'Start Maximized' is checked under the Project>Viewer dialog, then the project's Target System is likely set to an Embedded type but the runtime is on a full Windows installation.
To fix this, stop the project, go to Project>Options, and change the Target System from an Embedded type to the equivalent tag count Windows type, and click OK. Then start the project to make sure the Viewer is now starting maximized.