"Parameter is not valid" error when exiting

I noticed my system was slowing down, checked the CPU usage and found RDM was using around 30% so I decided to exit and restart the program (this happens a couple times a week). When I exited the program, instead of being prompted "do you really want to exit?", I received the following error:
Standard Edition 5.9.0.0
ArgumentException - Parameter is not valid.
at System.Drawing.Graphics.GetHdc()
at Devolutions.RemoteDesktopManager.Controls.TreeViewXP.WndProc(Message& message)
at System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m)
at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m)
at System.Windows.Forms.NativeWindow.Callback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)

I ended up killing the process through task manager as pressing the OK button simply redisplayed the error. Subsequent starts and exits of the program gave no errors. I guess this is more of an "FYI" than anything else...