Could not load file or assembly 'Telerik.Web.UI' or one of its dependencies. (Exception from HRESULT: 0x80131040)

DotNetNuke Error: "

Could not load file or assembly 'Telerik.Web.UI' or one of its dependencies. The located assembly's manifest definition does not match the assembly reference. (Exception from HRESULT: 0x80131040)".

PROBLEM
It is possible to receive the following error message after upgrading your web project with RadControls for ASP.NET AJAX to another version:
Could not load file or assembly 'Telerik.Web.UI, Version=XXXXX.X.XXXX.X, Culture=neutral, PublicKeyToken=XXXXXXXXXXXXX' or one of its dependencies. The located assembly's manifest definition does not match the assembly reference. (Exception from HRESULT: 0x80131040)

 

DESCRIPTION
The problem is due to the fact that the RadEditor's DialogHandler and SpellCheckHandlerhttpHandlers are registered in the web.config file with their fully qualified names and their versions are not updated.

SOLUTION
After upgrading your project to another version, you should update not only the Telerik.Web.UI.dll in the /bin folder, but also the DialogHandler and SpellCheckHandler httpHandlers declarations in web.config file as shown below:

<httphandlers>
      ...
      <add path="Telerik.Web.UI.DialogHandler.aspx" verb="*" type="Telerik.Web.UI.DialogHandler, Telerik.Web.UI, Version=2007.2.1107.0, Culture=neutral, PublicKeyToken=121fae78165ba3d4"
        validate="false" />
      <add path="Telerik.Web.UI.SpellCheckHandler.axd" verb="*" type="Telerik.Web.UI.SpellCheckHandler, Telerik.Web.UI, Version=2007.2.1107.0, Culture=neutral, PublicKeyToken=121fae78165ba3d4"
        validate="false" />

You should write the fully qualified names only if the Telerik.Web.UI.dll is registered in the GAC. If the Telerik.Web.UI.dll file is placed in the /bin folder of your project you can register theSpellCheckHandler httpHandlers in the web.config file with their short names, e.g.:

<httphandlers>
    ...
    <add path="Telerik.Web.UI.DialogHandler.aspx" verb="*" type="Telerik.Web.UI.DialogHandler, Telerik.Web.UI"
 validate="false" />
    <add path="Telerik.Web.UI.SpellCheckHandler.axd" verb="*" type="Telerik.Web.UI.SpellCheckHandler, Telerik.Web.UI"  validate="false" />

Additional information: If the RadControls for ASP.NET AJAX VSExtensions are installed then theDialogHandler and SpellCheckHandler handlers will be automatically registered in the web.config file when the Telerik > RadControls for ASP.NET AJAX > Upgrade Wizard menu is used.

Solution Provided by Tlererik.