problem with user page in admin

[KCarlson]

I have a new install I am working on, using a server at a client's location. I am having a problem I have never seen before. Everything seems to work fine, except when you go to the Manage Users page under people I get an error and the following in the application error log.
It looks like it is trying to use the .NET 3.5 web.config, even though I have the .NET 2 one in place in the root of this site. Has anyone else seen this?

Event code: 3006
Event message: A parser error has occurred.
Event time: 11/3/2009 4:25:36 PM
Event time (UTC): 11/3/2009 10:25:36 PM
Event ID: cbad9f76b9e1456aa5e42ea47ed8a7fe
Event sequence: 61
Event occurrence: 6
Event detail code: 0

Application information:
Application domain: /LM/W3SVC/718994839/Root-3-129017590228919855
Trust level: Full
Application Virtual Path: /
Application Path: D:\www\drsfn\wwwroot\
Machine name: ASKDRSEARSMSSQL

Process information:
Process ID: 6108
Process name: w3wp.exe
Account name: NT AUTHORITY\NETWORK SERVICE

Exception information:
Exception type: HttpParseException
Exception message: Unable to create type 'ajax:ModalPopupExtender'. Could not load file or assembly 'System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35' or one of its dependencies. The system cannot find the file specified.

Request information:
Request URL: http://drsfn.drsearsfamilyapproved.com/ ... fault.aspx
Request path: /Admin/People/Users/Default.aspx
User host address: 209.98.199.158
User: keith.carlson@plainwrapsolutions.com
Is authenticated: True
Authentication Type: Forms
Thread account name: NT AUTHORITY\NETWORK SERVICE

Thread information:
Thread ID: 9
Thread account name: NT AUTHORITY\NETWORK SERVICE
Is impersonating: False
Stack trace: at System.Web.UI.TemplateParser.ParseString(String text, VirtualPath virtualPath, Encoding fileEncoding)
at System.Web.UI.TemplateParser.ParseFile(String physicalPath, VirtualPath virtualPath)
at System.Web.UI.TemplateParser.ParseInternal()
at System.Web.UI.TemplateParser.Parse()
at System.Web.Compilation.BaseTemplateBuildProvider.get_CodeCompilerType()
at System.Web.Compilation.BuildProvider.GetCompilerTypeFromBuildProvider(BuildProvider buildProvider)
at System.Web.Compilation.BuildProvidersCompiler.ProcessBuildProviders()
at System.Web.Compilation.BuildProvidersCompiler.PerformBuild()
at System.Web.Compilation.BuildManager.CompileWebFile(VirtualPath virtualPath)
at System.Web.Compilation.BuildManager.GetVPathBuildResultInternal(VirtualPath virtualPath, Boolean noBuild, Boolean allowCrossApp, Boolean allowBuildInPrecompile)
at System.Web.Compilation.BuildManager.GetVPathBuildResultWithNoAssert(HttpContext context, VirtualPath virtualPath, Boolean noBuild, Boolean allowCrossApp, Boolean allowBuildInPrecompile)
at System.Web.Compilation.BuildManager.GetVirtualPathObjectFactory(VirtualPath virtualPath, HttpContext context, Boolean allowCrossApp, Boolean noAssert)
at System.Web.Compilation.BuildManager.CreateInstanceFromVirtualPath(VirtualPath virtualPath, Type requiredBaseType, HttpContext context, Boolean allowCrossApp, Boolean noAssert)
at System.Web.UI.PageHandlerFactory.GetHandlerHelper(HttpContext context, String requestType, VirtualPath virtualPath, String physicalPath)
at System.Web.UI.PageHandlerFactory.System.Web.IHttpHandlerFactory2.GetHandler(HttpContext context, String requestType, VirtualPath virtualPath, String physicalPath)
at System.Web.HttpApplication.MapHttpHandler(HttpContext context, String requestType, VirtualPath path, String pathTranslated, Boolean useAppConfig)
at System.Web.HttpApplication.MapHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute()
at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously)


Custom event details:

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[jmestep]

It looks like it could be a mis-match, like you are suggesting. I ran into that once in a upgrade and it was a matter of using the old code- I think the site didn't have the new one on it. I just don't remember the specifics, though.

[KCarlson]

I have confirmed that everywhere that modalpopupextender is used I get that error and the entry in the application log. So it seems like something is amiss with the ajax possibly, but I can't figure out why only that one would be erroring.

[mazhar]

Make sure that during upgrade Bin folder is updated correctly, it may be something due to unsuccessful upgrade.