Javascript errors after upgrading to .NET 4.0

I have inherited a working VB.NET 2.0 web app that has several User Controls 开发者_StackOverflow中文版with GridViews inside Update Panels. After running the VS 2010 Upgrade Wizard, the app runs fine in the debugger except for a couple of these Gridviews. In these, update and delete work but adding a new item causes the following javascript error when Save is clicked (calling DoPostBackWithOptions):

Microsoft jscript runtime error 
Sys.WebForms.PageRequestManagerServerErrorException: Index was out of range. Must be non-negative and less than the size of the collection.
Parameter name: index

My theory is that the code is fine (I haven't touched it) and that there is some sort of configuration issue causing this. I have looked through SO and elsewhere and have tweaked my web config and updated the Ajax toolkit assembly. I got nowhere stepping thru the ScriptResource.axd javascript throwing the error. Any suggestions?

Update

The app works fine if I upgrade it to .NET 3.5 using the VS 2008 wizard. However, if I then upgrade that to 4.0 with VS 2010 the problem resurfaces.

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Have you tried setting the controlRenderingCompatibilityVersion? The upgrade process should have included it for you, but it might be the cause of your heartache. It's in the <pages... tag of your web.config file...

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This is only a workaround not a fix. But I figured I'd add it to help anyone else that might have a similar issue.

What I have figured out is that the project upgrades to .NET 3.5 just fine but that going 4.0 breaks it. I am not sure if the framework breaks it or the upgrade wizard does.

So the successful path for me has been:

1. Open in VS 2008 and run the upgrade wizard to upgrade to 3.5.
2. Open the project again in VS 2010 and run the upgrade wizard but opt to leave it on the 3.5 framework.

At this point the project behaves fine and I can used VS 2010 to make my updates.