Okay, I found the problem. It looks like the Project Upgrade Wizard did not work completely (maybe a Source Control issue). I manually replaced some Infragistics2 references with Infragistics35 references and it works now.

It was hard to find this since most of the older Infragistics controls didn't seem to care that they were 2.0 assemblies loded into a 3.5 environment, only the newer controls were picky about it.

Thank you for your help.

Unfortunately, it seems to work in a simple example, but not in my existing application which is quite complex.

I did not have this problem before switching from .NET 2.0 to .NET 3.5. The exact same code worked in 2.0, but now I get this error in 3.5. All other functionality, (Ajax, UpdatePanels, WARP panels, other Infragistics controls, etc.) are working fine. The only problem I see is with the WebDialogWindow.

When I remove the WebDialogWindow, the error goes away. I do not get the error from any other Infragistics controls on the UserControl (UltraWebGrid, UltraWebGridExcelExporter, WebDateChooser).

Is there another Infragistics control you can suggest I can try to put on the UserControl to see if it is just with the WebDialogWindow control that has the problem?

I also have this issue.

'This Infragistics control requires a ScriptManager object on the page in order to operate correctly.'

I have a ScriptManager on the master page, a ScriptManagerProxy on the UserControl, and a WebDialogWindow on the UserControl.

I am targeting .NET Framework 3.5.