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We have observed that when when using our software (with a recently integrated Ribbon) on Windows XP, a NullReferenceException is thrown from inside the message loop, which causes the application to crash. We are using v4.2 of the Elegant Ribbon. Here is the stack trace:

Object reference not set to an instance of an object.

at Elegant.Ui.Ribbon.??(InputSpyMouseEventArgs ?)
at Elegant.Ui.Ribbon.?.? ???(InputSpyMouseEventArgs ?)
at Elegant.Ui.InputSpy.NotifyAboutMouseUpEvent(IInputSpyMouseListener[] listeners, MouseButtons buttons, Int32 x, Int32 y, IntPtr hwnd)
at Elegant.Ui.InputSpy.MouseHookProc(Int32 nCode, IntPtr wParam, IntPtr lParam)
at System.Windows.Forms.UnsafeNativeMethods.PeekMessage(MSG& msg, HandleRef hwnd, Int32 msgMin, Int32 msgMax, Int32 remove)
at System.Windows.Forms.Application.ComponentManager.System.Windows.Forms.UnsafeNativeMethods.IMsoComponentManager.FPushMessageLoop(IntPtr 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 com.alibre.app.ApplicationHost.run()
at com.alibre.client.ClientContext.runLaunch()
at com.alibre.client.ClientContext.run()
at com.alibre.app.Client.Main(String[] arguments)


As you can see, it seems to implicate the Ribbon framework here. (In the top two lines, there were some weird characters--presumeably obfuscated class/method names--that did not paste through.)

We are still working on figuring out exactly what action is triggering it and what steps can be used to reproduce it. However, it has reproduced on each of the Windows XP systems we have tried it on so far, and none of the computers running Vista or 7. It seems to be somewhat random, as it has been observed to occur anywhere from once every 4 hours to 5 times in one hour. When the Ribbon is turned off in our software, it no longer occurs.

Any idea what might be going on here? We’re still trying to get a better understanding of it, but given that it’s happening in the Ribbon internals, it’s hard for us to debug. Any help would be appreciated.

Object reference not set to an instance of an object