Is there any reason to think that any of those changes would impact the error in question? After all, it doesn't happen early on, and removing that entire block of code has no impact on the error.

In general, I've been reluctant to use LINQ in this project, though my objection doesn't stand in this particular case. Much of this program consists of models that will be exposed via interfaces for the use of others. I have no idea how efficient those others will be, nor any control on that, so I squeezed as much speed as I could out of the models, which included squeezing out all LINQ. However, this particular block of code is not part of any model, and is nothing more than a very rarely frequented form that might show up on startup under just the right circumstances, so I can do whatever I want with this part.

Here are a couple points:
When I look at the exception details, the StackTrace is Nothing. However, this is the stack trace at the time the exception happens:

System.Windows.Forms.dll!System.Windows.Forms.AccessibleObject.Accessibility.IAccessible.get_accChil d(object childID) Unknown
System.Windows.Forms.dll!System.Windows.Forms.InternalAccessibleObject.System.Windows.Forms.UnsafeNa tiveMethods.IAccessibleInternal.get_accChild(object childID) Unknown
[Native to Managed Transition]
[Managed to Native Transition]
System.Windows.Forms.dll!System.Windows.Forms.NativeWindow.DefWndProc(ref System.Windows.Forms.Message m) Unknown
System.Windows.Forms.dll!System.Windows.Forms.Control.DefWndProc(ref System.Windows.Forms.Message m) Unknown
System.Windows.Forms.dll!System.Windows.Forms.Control.WmSetFocus(ref System.Windows.Forms.Message m) Unknown
System.Windows.Forms.dll!System.Windows.Forms.Control.WndProc(ref System.Windows.Forms.Message m) Unknown
System.Windows.Forms.dll!System.Windows.Forms.ListBox.WndProc(ref System.Windows.Forms.Message m) Unknown
System.Windows.Forms.dll!System.Windows.Forms.Control.ControlNativeWindow.OnMessage(ref System.Windows.Forms.Message m) Unknown
System.Windows.Forms.dll!System.Windows.Forms.Control.ControlNativeWindow.WndProc(ref System.Windows.Forms.Message m) Unknown
System.Windows.Forms.dll!System.Windows.Forms.NativeWindow.DebuggableCallback(System.IntPtr hWnd, int msg, System.IntPtr wparam, System.IntPtr lparam) Unknown
[Native to Managed Transition]
[Managed to Native Transition]
System.Windows.Forms.dll!System.Windows.Forms.ContainerControl.FocusActiveControlInternal() Unknown
System.Windows.Forms.dll!System.Windows.Forms.Form.Active.set(bool value) Unknown
System.Windows.Forms.dll!System.Windows.Forms.Form.WmActivate(ref System.Windows.Forms.Message m) Unknown
System.Windows.Forms.dll!System.Windows.Forms.Form.WndProc(ref System.Windows.Forms.Message m) Unknown
System.Windows.Forms.dll!System.Windows.Forms.Control.ControlNativeWindow.OnMessage(ref System.Windows.Forms.Message m) Unknown
System.Windows.Forms.dll!System.Windows.Forms.Control.ControlNativeWindow.WndProc(ref System.Windows.Forms.Message m) Unknown
System.Windows.Forms.dll!System.Windows.Forms.NativeWindow.DebuggableCallback(System.IntPtr hWnd, int msg, System.IntPtr wparam, System.IntPtr lparam) Unknown
[Native to Managed Transition]
[Managed to Native Transition]
System.Windows.Forms.dll!System.Windows.Forms.Control.SetVisibleCore(bool value) Unknown
System.Windows.Forms.dll!System.Windows.Forms.Form.SetVisibleCore(bool value) Unknown
System.Windows.Forms.dll!System.Windows.Forms.Control.Visible.set(bool value) Unknown
System.Windows.Forms.dll!System.Windows.Forms.Application.ThreadContext.RunMessageLoopInner(int reason, System.Windows.Forms.ApplicationContext context) Unknown
System.Windows.Forms.dll!System.Windows.Forms.Application.ThreadContext.RunMessageLoop(int reason, System.Windows.Forms.ApplicationContext context) Unknown
System.Windows.Forms.dll!System.Windows.Forms.Application.RunDialog(System.Windows.Forms.Form form) Unknown
System.Windows.Forms.dll!System.Windows.Forms.Form.ShowDialog(System.Windows.Forms.IWin32Window owner) Unknown
System.Windows.Forms.dll!System.Windows.Forms.Form.ShowDialog() Unknown
> HIS.exe!HIS.StartUpForm.FinishSetup() Line 114 Basic
The very bottom line of that is the method that shows the form (FinishSetup()).

I'm about to head out to a beautiful mountain stream in one of the most scenic places in the world, to stagger through a meadow along the banks of said stream for the purpose of counting spawning salmon. I'll be back in eight hours, or so, but out of communication until then.