I just upgraded my localhost development pc to DNN 4.9, now when I click on my XMod IDE tab I get:

A critical error has occurred.
Operation is not valid due to the current state of the object.

the log viewer shows:

AssemblyVersion: 04.09.00
PortalID: 0
PortalName: My Website
UserID: 1
UserName: host
ActiveTabID: 63
ActiveTabName: xmod ide
RawURL: /dotnetnuke/xmodide.aspx
AbsoluteURL: /dotnetnuke/Default.aspx
AbsoluteURLReferrer: http://localhost/dotnetnuke/
UserAgent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-GB; rv:1.9.0.1) Gecko/2008070208 Firefox/3.0.1
DefaultDataProvider: DotNetNuke.Data.SqlDataProvider, DotNetNuke.SqlDataProvider
ExceptionGUID: d818959b-2cb3-452d-bdfb-3c2dede722a6
InnerException: Operation is not valid due to the current state of the object.
FileName:
FileLineNumber: 0
FileColumnNumber: 0
Method: Adequation.XMod.IDE.Components.DocumentTree.EnsureNodesForPath
StackTrace:
Message: DotNetNuke.Services.Exceptions.PageLoadException: Operation is not valid due to the current state of the object. ---> System.InvalidOperationException: Operation is not valid due to the current state of the object. at Adequation.XMod.IDE.Components.DocumentTree.EnsureNodesForPath(RadTreeNodeCollection nodes, String[] path, Int32 level) at Adequation.XMod.IDE.Components.DocumentTree.EnsureNodesForPath(RadTreeNodeCollection nodes, String[] path, Int32 level) at Adequation.XMod.IDE.Components.DocumentTree.EnsureNodesForPath(RadTreeNodeCollection nodes, String[] path, Int32 level) at Adequation.XMod.IDE.Components.DocumentTree.AddNode(RadTreeNode node, String[] path) at Adequation.XMod.IDE.Components.SiteBrowser.Page_Load(Object sender, EventArgs e) at System.Web.Util.CalliHelper.EventArgFunctionCaller(IntPtr fp, Object o, Object t, EventArgs e) at System.Web.Util.CalliEventHandlerDelegateProxy.Callback(Object sender, EventArgs e) at System.Web.UI.Control.OnLoad(EventArgs e) at System.Web.UI.Control.LoadRecursive() at System.Web.UI.Control.LoadRecursive() at System.Web.UI.Control.LoadRecursive() at System.Web.UI.Control.LoadRecursive() at System.Web.UI.Control.LoadRecursive() at System.Web.UI.Control.LoadRecursive() at System.Web.UI.Control.LoadRecursive() at System.Web.UI.Control.LoadRecursive() at System.Web.UI.Control.LoadRecursive() at System.Web.UI.Control.LoadRecursive() at System.Web.UI.Control.LoadRecursive() at System.Web.UI.Control.LoadRecursive() at System.Web.UI.Control.LoadRecursive() at System.Web.UI.Control.LoadRecursive() at System.Web.UI.Control.LoadRecursive() at System.Web.UI.Control.LoadRecursive() at System.Web.UI.Control.LoadRecursive() at System.Web.UI.Control.LoadRecursive() at System.Web.UI.Control.LoadRecursive() at System.Web.UI.Control.LoadRecursive() at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) --- End of inner exception stack trace ---
Source:

Any ideas?

After some basic testing with 4.9.0, everything looks fine. However, we did the test with a beta version of XMod IDE 2.0.

The problem you are getting is related to your site's structure. Since it is not a publicly visible install, would it be possible for you to send us a copy of your site, with the database, you we can install and test locally and determine what exactly in your site's structure is triggering the error?

Thank you,

Etienne