Object reference not set to an instance of an object in visual studio designer

I have Visual Studio 2026 with Infragistics 26.1. When I stop debugging my application and open the Form Designer, I get the following error:

“Object reference not set to an instance of an object.”

I checked the Output window and found the following stack trace:

System.NullReferenceException: Object reference not set to an instance of an object.
                           at Infragistics.Win.Design.Designers.UltraPanelClientAreaProxyDesigner.OnSelectionChanged(Object sender, EventArgs e) in E:\BuildAgents\B\_work\33\s\dev-tools\WinForms\Main\Source\Misc\DesignTools.Client\Designers\Panel\UltraPanelClientAreaProxyDesigner.cs:line 66
                           at System.EventHandler.Invoke(Object sender, EventArgs e)
                           at Microsoft.VisualStudio.WinForms.DesignSurfaceService.DisconnectSession(Boolean forcibleDisconnection)
                           at Microsoft.VisualStudio.WinForms.VSDesignSurface.<RecreateDesignerSessionAsync>d__22.MoveNext()
                        --- End of stack trace from previous location where exception was thrown ---
                           at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
                           at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
                           at Microsoft.VisualStudio.WinForms.ProjectWatchers.ProjectWatcherService.ProjectWatcher.<>c__DisplayClass70_1.<<RestartServerProcessAndReloadDesignerIfRequired>g__RecreateDesignerSessionAndReloadDesignerAsync|1>d.MoveNext()
                        --- End of stack trace from previous location where exception was thrown ---
                           at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
                           at Microsoft.VisualStudio.WinForms.ProjectWatchers.ProjectWatcherService.ProjectWatcher.<>c__DisplayClass70_1.<<RestartServerProcessAndReloadDesignerIfRequired>g__RecreateDesignerSessionAndReloadDesignerAsync|1>d.MoveNext()
                        --- End of stack trace from previous location where exception was thrown ---
                           at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
                           at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
                           at Microsoft.VisualStudio.WinForms.ProjectWatchers.ProjectWatcherService.ProjectWatcher.<>c__DisplayClass70_0.<<RestartServerProcessAndReloadDesignerIfRequired>b__0>d.MoveNext()

This happens specifically when I stop the application and then open the Form Designer.

Hello Quid,

Thank you for contacting Infragistics Developer Support.

I have been investigating into the behavior you are seeing, and I have a few questions for you on this matter, as I have not yet been able to reproduce this issue. Can you please provide an answer to the following?

1. What version of .NET Framework / .NET Core are you targeting in your application?
2. It looks like the exception is coming from an UltraPanel. Do you have more details on how you are using the UltraPanel in your application?

Please let me know if you have any other questions or concerns on this matter.

Hi, thanks for your answer.

The application is built with .NET 10.

I have attached an example of a form and a video. Sometimes the message “Object reference not set to an instance of an object” appears when I close the runtime and open the designer, but the error is always visible in the Output window.

thancks Tommaso