ceyhun@ceyhun-O-E-M:~/openbve$ mono OpenBve.exe
System.NullReferenceException: Object reference not set to an instance of an object
at System.Windows.Forms.ListView+ItemControl.ItemsMouseDown (System.Object sender, System.Windows.Forms.MouseEventArgs me) [0x00000] in <filename unknown>:0
at System.Windows.Forms.Control.OnMouseDown (System.Windows.Forms.MouseEventArgs e) [0x00000] in <filename unknown>:0
at System.Windows.Forms.Control.WmLButtonDown (System.Windows.Forms.Message& m) [0x00000] in <filename unknown>:0
at System.Windows.Forms.Control.WndProc (System.Windows.Forms.Message& m) [0x00000] in <filename unknown>:0
at System.Windows.Forms.ListView+ItemControl.WndProc (System.Windows.Forms.Message& m) [0x00000] in <filename unknown>:0
at System.Windows.Forms.Control+ControlWindowTarget.OnMessage (System.Windows.Forms.Message& m) [0x00000] in <filename unknown>:0
at System.Windows.Forms.Control+ControlNativeWindow.WndProc (System.Windows.Forms.Message& m) [0x00000] in <filename unknown>:0
at System.Windows.Forms.NativeWindow.WndProc (IntPtr hWnd, Msg msg, IntPtr wParam, IntPtr lParam) [0x00000] in <filename unknown>:0
ceyhun@ceyhun-O-E-M:~/openbve$
This doesn't look like you installed OpenBVE from the Ubuntu repositories or did you?
What release of Ubuntu are you using?