System.Reflection.TargetInvocationException was unhandled
  Message="Exception has been thrown by the target of an invocation."
  Source="mscorlib"
  StackTrace:
       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.Forms.Control.InvokeMarshaledCallbackDo(ThreadMethodEntry tme)
       at System.Windows.Forms.Control.InvokeMarshaledCallbackHelper(Object obj)
       at System.Threading.ExecutionContext.runTryCode(Object userData)
       at System.Runtime.CompilerServices.RuntimeHelpers.ExecuteCodeWithGuaranteedCleanup(TryCode code, CleanupCode backoutCode, Object userData)
       at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state)
       at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
       at System.Windows.Forms.Control.InvokeMarshaledCallback(ThreadMethodEntry tme)
       at System.Windows.Forms.Control.InvokeMarshaledCallbacks()
       at System.Windows.Forms.Control.WndProc(Message& m)
       at System.Windows.Forms.ScrollableControl.WndProc(Message& m)
       at System.Windows.Forms.ContainerControl.WndProc(Message& m)
       at System.Windows.Forms.Form.WndProc(Message& m)
       at System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m)
       at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m)
       at System.Windows.Forms.NativeWindow.DebuggableCallback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)
       at System.Windows.Forms.UnsafeNativeMethods.DispatchMessageW(MSG& msg)
       at System.Windows.Forms.Application.ComponentManager.System.Windows.Forms.UnsafeNativeMethods.IMsoComponentManager.FPushMessageLoop(Int32 dwComponentID, Int32 reason, Int32 pvLoopData)
       at System.Windows.Forms.Application.ThreadContext.RunMessageLoopInner(Int32 reason, ApplicationContext context)
       at System.Windows.Forms.Application.ThreadContext.RunMessageLoop(Int32 reason, ApplicationContext context)
       at System.Windows.Forms.Application.Run(Form mainForm)
       at ClassMonitor.Program.Main() in C:\Users\Corey\Documents\Visual Studio 2008\Projects\ClassMonitor\WindowsFormsApplication1\Program.cs:line 13
       at System.AppDomain._nExecuteAssembly(Assembly assembly, String[] args)
       at System.AppDomain.ExecuteAssembly(String assemblyFile, Evidence assemblySecurity, String[] args)
       at Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly()
       at System.Threading.ThreadHelper.ThreadStart_Context(Object state)
       at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
       at System.Threading.ThreadHelper.ThreadStart()
  InnerException: System.ArgumentOutOfRangeException
       Message="InvalidArgument=Value of '-1' is not valid for 'index'.\r\nParameter name: index"
       Source="System.Windows.Forms"
       ParamName="index"
       StackTrace:
            at System.Windows.Forms.ComboBox.ObjectCollection.SetItemInternal(Int32 index, Object value)
            at System.Windows.Forms.ComboBox.ObjectCollection.set_Item(Int32 index, Object value)
            at ClassMonitor.MainForm.modifyCombo(ClassInfoHolder oldClass, ClassInfoHolder newClass) in C:\Users\Corey\Documents\Visual Studio 2008\Projects\ClassMonitor\WindowsFormsApplication1\MainForm.cs:line 249
            at ClassMonitor.MainForm.<>c__DisplayClass4.<monitorClass>b__0() in C:\Users\Corey\Documents\Visual Studio 2008\Projects\ClassMonitor\WindowsFormsApplication1\MainForm.cs:line 265
       InnerException: