Hello Malcom: 

First, welcome to the community website and thank you for your question!  :)  

By the way...  Did you know there are two DNN conferences coming up?  DNN Summit in February, and DNN-Connect in May.  :)

Anyhow, there could be any number of things going wrong with this website.  More troubleshooting will be necessary.  

Since this is a fatal error that appears to be crashing the application pool. you'll want to look through the WIndows Event Log and find any critical errors that appear related and diagnose them.  Clear out any and all related errors you can, so you know they're not the root cause.  

Next, do the same thing with the DNN log, but use the Log4NET log file, not the Admin Logs.  There will be more information there.  You can find those log files at the path noted below.  

/Portals/_default/Logs/*.resources

Start from the bottom of the file, and being diagnosing and resolving each related error that you can.  Once you've done that, begin troubleshooting and testing again.  

This should help you get to the root cause and resolve the issue.  Once you do, I'd recommend triaging and resolving all remaining exceptions that you also saw while trying to fix this.  If they stay, you'll end up in an inconvenient moment like right now again.  :) 

Hey Malcolm: 

The video below will help introduce you to the admin logs and Log4NET logs.  

https://www.youtube.com/watch?v=uyNebzEy8Bk

Many thanks Will I'll take a look and see what I can find.

Hi Will - I have this error - can you think of anything to help resolve this?

2023-01-27 08:00:35,310 [yellow][Thread:12][FATAL] DotNetNuke.Framework.PageBase - An error has occurred while loading page.
System.Web.HttpParseException (0x80004005): The base class includes the field 'controlBar_SwitchSite', but its type (System.Web.UI.WebControls.DropDownList) is not compatible with the type of control (DotNetNuke.Web.UI.WebControls.DnnComboBox).

Here's the full text below...

2023-01-27 08:22:47,319 [yellow][Thread:20][FATAL] DotNetNuke.Framework.PageBase - An error has occurred while loading page.
System.Web.HttpParseException (0x80004005): The base class includes the field 'controlBar_SwitchSite', but its type (System.Web.UI.WebControls.DropDownList) is not compatible with the type of control (DotNetNuke.Web.UI.WebControls.DnnComboBox). ---> System.Web.HttpParseException (0x80004005): The base class includes the field 'controlBar_SwitchSite', but its type (System.Web.UI.WebControls.DropDownList) is not compatible with the type of control (DotNetNuke.Web.UI.WebControls.DnnComboBox).
   at System.Web.Compilation.BaseTemplateCodeDomTreeGenerator.BuildFieldDeclaration(ControlBuilder builder)
   at System.Web.Compilation.BaseTemplateCodeDomTreeGenerator.BuildSourceDataTreeFromBuilder(ControlBuilder builder, Boolean fInTemplate, Boolean topLevelControlInTemplate, PropertyEntry pse)
   at System.Web.Compilation.BaseTemplateCodeDomTreeGenerator.BuildSourceDataTreeFromBuilder(ControlBuilder builder, Boolean fInTemplate, Boolean topLevelControlInTemplate, PropertyEntry pse)
   at System.Web.Compilation.BaseTemplateCodeDomTreeGenerator.BuildSourceDataTreeFromBuilder(ControlBuilder builder, Boolean fInTemplate, Boolean topLevelControlInTemplate, PropertyEntry pse)
   at System.Web.Compilation.TemplateControlCodeDomTreeGenerator.BuildMiscClassMembers()
   at System.Web.Compilation.BaseCodeDomTreeGenerator.BuildSourceDataTree()
   at System.Web.Compilation.BaseCodeDomTreeGenerator.GetCodeDomTree(CodeDomProvider codeDomProvider, StringResourceBuilder stringResourceBuilder, VirtualPath virtualPath)
   at System.Web.Compilation.BaseTemplateBuildProvider.GenerateCode(AssemblyBuilder assemblyBuilder)
   at System.Web.Compilation.AssemblyBuilder.AddBuildProvider(BuildProvider buildProvider)
   at System.Web.Compilation.AssemblyBuilder.AddBuildProvider(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, Boolean throwIfNotFound, Boolean ensureIsUpToDate)
   at System.Web.Compilation.BuildManager.GetVPathBuildResultWithNoAssert(HttpContext context, VirtualPath virtualPath, Boolean noBuild, Boolean allowCrossApp, Boolean allowBuildInPrecompile, Boolean throwIfNotFound, Boolean ensureIsUpToDate)
   at System.Web.UI.TemplateControl.LoadControl(VirtualPath virtualPath)
   at DotNetNuke.UI.ControlUtilities.LoadControl[T](TemplateControl containerControl, String ControlSrc)
   at DotNetNuke.UI.Skins.Skin.InjectControlPanel()
   at DotNetNuke.UI.Skins.Skin.OnInit(EventArgs e)
   at System.Web.UI.Control.InitRecursive(Control namingContainer)
   at System.Web.UI.Control.AddedControl(Control control, Int32 index)
   at DotNetNuke.Framework.DefaultPage.OnInit(EventArgs e)
   at System.Web.UI.Control.<InitRecursiveAsync>d__225.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 System.Web.Util.WithinCancellableCallbackTaskAwaitable.WithinCancellableCallbackTaskAwaiter.GetResult()
   at System.Web.UI.Page.<ProcessRequestMainAsync>d__523.MoveNext()

This appears to be a pretty straightforward error message, but I'm not sure what would cause it. 

What it seems to be is that a control named "SwitchSite" somewhere is in a view, but of type "DropDownList" when the source code is expecting the dropdown list to be of type "DnnComboBox" instead. 

I wouldn't be able to help point you to where to find this, but the video below might be able to help you figure that out.  

https://www.youtube.com/w...?v=5yoJeAKWQGM  (the link skips to the part where I use FileLocator to find things)

Ideally, you'll find this in some new code you've introduced at some point, like in the theme, a module, a persona bar extension, etc. 

Hopefully, this issue isn't a core code change getting in the way.  🤞🏽 

Again, many thanks for your help Will - I'll certainly check this out and see where I get to.

Hi Will I used the File Locator Lite version and found the "SwitchSite" referenced in the wwwroot/Admin/ControlPanel/SwitchSite.ACSX file.

I was expecting from what you'd written to find reference to a dropdownlist but instead found DnnComboBox in the code...

<%@ Control language="C#" AutoEventWireup="false" Inherits="DotNetNuke.UI.ControlPanel.SwitchSite" Codebehind="SwitchSite.ascx.cs" %>
<%@ Register Assembly="Telerik.Web.UI" Namespace="Telerik.Web.UI" TagPrefix="telerik" %>
<%@ Register TagPrefix="dnn" Namespace="DotNetNuke.Web.UI.WebControls" Assembly="DotNetNuke.Web" %>
<%@ Register TagPrefix="dnn" Namespace="DotNetNuke.Web.UI.WebControls" Assembly="DotNetNuke.Web.Deprecated" %>
<%--<asp:DropDownList ID="SitesLst" runat="server" MaxHeight="300px" Width="200px" />--%>
<dnn:DnnComboBox ID="SitesLst" runat="server" />
<asp:LinkButton ID="cmdSwitch" runat="server" ResourceKey="SwitchButton" CausesValidation="false" CssClass="dnnSecondaryAction selectAction" />

Rather than continue the chase to find what's wrong would I be best to simply re-create the site on a new installation?  There's only around 10 or so pages.  If so is there a relatively easy way to move the skin files to the new installation?  I'm not too worried about the content as I can always copy & paste then adjust the CSS to match.

Many thanks for your help Will I really appreciate it.

Bye for now
Malcolm

What version of DNN are you working with right now? The path that you've posted is a core path in DNN. So it sounds like you either removed Telerik from your website too early, or there might be core code changes (potentially making this a very complicated situation).

Hi Will - the site is running 9.10. I haven't removed telerik knowingly myself and seeing you write as you did makes me think another installation and manually copy the content may be the best option.

The thing that worries me is being able to get the skin files across to another installation successfully as I don't have the original skin files I loaded onto the site.  I take it it isn't as easy as simply copying the skin files via FTP then re-uploading them to the new installation.

Bye for now
Malcolm