If you don't already have a saved game...
- Launch Supremacy
- Create a new game and save it
- Exit Supremacy

Now to the crash bug...
- Launch Supremacy
- Create a new game and retire
- Load a saved game

or
- Launch Supremacy
- Load a saved game and retire
- Load a saved game


Supremacy will crash every time you attempt to load a game if you don't completely exit Supremacy between games.

Actually I just managed to crash the game by
1) Starting a new game
2) Saving and then retiring
3) Starting a new game again

Then an "Unhandled exception" error popped up and Supremacy died...

The error file is this:

Exception has been thrown by the target of an invocation.

at System.RuntimeMethodHandle._InvokeMethodFast(Object target, Object[] arguments, SignatureStruct& sig, MethodAttributes methodAttributes, RuntimeTypeHandle typeOwner)
at System.RuntimeMethodHandle.InvokeMethodFast(Object target, Object[] arguments, Signature sig, MethodAttributes methodAttributes, RuntimeTypeHandle typeOwner)
at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture, Boolean skipVisibilityChecks)
at System.Delegate.DynamicInvokeImpl(Object[] args)
at System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, Object args, Boolean isSingleParameter)
at System.Windows.Threading.ExceptionWrapper.TryCatchWhen(Object source, Delegate callback, Object args, Boolean isSingleParameter, Delegate catchHandler)

----------------------------------------

Object reference not set to an instance of an object.

at Supremacy.Client.ClientApp.ReloadResources() in C:\Users\mikest\Workspace\supremacy\Mainline\SupremacyClient\ClientApp.xaml.cs:line 166

----------------------------------------

Exception has been thrown by the target of an invocation.

at System.RuntimeMethodHandle._InvokeMethodFast(Object target, Object[] arguments, SignatureStruct& sig, MethodAttributes methodAttributes, RuntimeTypeHandle typeOwner)
at System.RuntimeMethodHandle.InvokeMethodFast(Object target, Object[] arguments, Signature sig, MethodAttributes methodAttributes, RuntimeTypeHandle typeOwner)
at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture, Boolean skipVisibilityChecks)
at System.Delegate.DynamicInvokeImpl(Object[] args)
at System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, Object args, Boolean isSingleParameter)
at System.Windows.Threading.ExceptionWrapper.TryCatchWhen(Object source, Delegate callback, Object args, Boolean isSingleParameter, Delegate catchHandler)

----------------------------------------

Object reference not set to an instance of an object.

at Supremacy.Client.SystemScreen..ctor() in C:\Users\mikest\Workspace\supremacy\Mainline\SupremacyClient\SystemScreen.cs:line 176
at Supremacy.Client.GameWindow.CreateGameScreens() in C:\Users\mikest\Workspace\supremacy\Mainline\SupremacyClient\GameWindow.xaml.cs:line 876

----------------------------------------

That's basically the same error I'm getting. And another way to reproduce it.

For now, rule of thumb, quit and restart Supremacy when you want to switch to a different game.

Confirmed, I've been able to reproduce this as well. Thanks for the report!