It looks like you are experiencing a version issue with the Ajax Control Toolkit. You can download the binary you need from here:

http://ajaxcontroltoolkit.codeplex.co...

Make a backup copy of the current version of AjaxControlToolkit.dll in your ~\bin folder. Right click properties to verify the version number. Then unzip the file downloaded above and just drop the AjaxControlToolkit.dll file in your ~\bin folder. This should fix your problem.

Update: You may want to read this thread.

http://www.smith-consulting.com/forum...

I'm sorry, I made a mistake, the file should be installed by SmithCart, but depending on your hosting environment and Ajax configuration, web.config may require manual modifications to make it work properly. Different Ajax versions have always been a problem for ASP.NET. If SmithCart forced its version it could break other modules. On the other hand if another module forced its version, it could break other modules including SmithCart.

The clue here is "manifest definition does not match the assembly reference". This means your web.config is configured with a specific version that is different than the file.

You will probably need to add this to the assemblyBinding section in web.config

<dependentAssembly>

<assemblyIdentity name="AjaxControlToolkit" publicKeyToken="28f01b0e84b6d53e" />

<bindingRedirect oldVersion="1.0.20229.20821" newVersion="3.0.30930.28736" />

</dependentAssembly>

I hope this is of some help to you.