Well I guess here's my answer.  I have 3.0.11119 installed, and here's what I get:

DotNetNuke.Services.Exceptions.ModuleLoadException: Could not load file or assembly 'AjaxControlToolkit, Version=1.0.10920.32880, Culture=neutral, PublicKeyToken=28f01b0e84b6d53e' or one of its dependencies. The located assembly's manifest definition does not match the assembly reference. (Exception from HRESULT: 0x80131040) ---> System.Web.HttpParseException: Could not load file or assembly 'AjaxControlToolkit, Version=1.0.10920.32880, Culture=neutral, PublicKeyToken=28f01b0e84b6d53e' or one of its dependencies. The located assembly's manifest definition does not match the assembly reference. (Exception from HRESULT: 0x80131040) ---> System.IO.FileLoadException: Could not load file or assembly 'AjaxControlToolkit, Version=1.0.10920.32880, Culture=neutral, PublicKeyToken=28f01b0e84b6d53e' or one of its dependencies. The located assembly's manifest definition does not match the assembly reference. (Exception from HRESULT: 0x80131040) File name: 'AjaxControlToolkit, Version=1.0.10920.32880, Culture=neutral, PublicKeyToken=28f01b0e84b6d53e' at System.Signature._GetSignature(SignatureStruct& signature, Void* pCorSig, Int32 cCorSig, IntPtr fieldHandle, IntPtr methodHandle, IntPtr declaringTypeHandle) at System.Signature.GetSignature(SignatureStruct& signature, Void* pCorSig, Int32 cCorSig, RuntimeFieldHandle fieldHandle, RuntimeMethodHandle methodHandle, RuntimeTypeHandle declaringTypeHandle) at System.Signature..ctor(RuntimeFieldHandle fieldHandle, RuntimeTypeHandle declaringTypeHandle) at System.Reflection.RtFieldInfo.get_FieldType() at System.Web.UI.Util.GetNonPrivateFieldType(Type classType, String fieldName) 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.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.BaseTemplateBuildProvider.GenerateCode(AssemblyBuilder assemblyBuilder) at System.Web.Compilation.AssemblyBuilder.AddBuildProvider(BuildProvider buildProvider) WRN: Assembly binding logging is turned OFF. To enable assembly bind failure logging, set the registry value [HKLM\Software\Microsoft\Fusion!EnableLog] (DWORD) to 1. Note: There is some performance penalty associated with assembly bind failure logging. To turn this feature off, remove the registry value [HKLM\Software\Microsoft\Fusion!EnableLog]. --- End of inner exception stack trace --- 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) at System.Web.Compilation.BuildManager.GetVPathBuildResultWithNoAssert(HttpContext context, VirtualPath virtualPath, Boolean noBuild, Boolean allowCrossApp, Boolean allowBuildInPrecompile) at System.Web.UI.TemplateControl.LoadControl(VirtualPath virtualPath) at System.Web.UI.TemplateControl.LoadControl(String virtualPath) at Engage.Dnn.Publish.ItemDisplay.LoadControlType() --- End of inner exception stack trace ---

Unfortunately when we compile Publish against the 9/20 release for some reason the newer releases won't work. I'm not sure why, but I believe it has something to do with the way the toolkits are compiled.

Shoot me an email and I can see about compiling you a special version of the module. We'll be putting a 05.00.01 release out later this week but aren't likely to do a public recompile using a newer version of the Toolkit for another release or two.

chammond - engagesoftware.net

I just downloaded and installed Publish 5.0.0 yesterday and installed AJAX toolkit 1.0.20229  and am seeing the same exact error.  I really don't want to have to reinstall DNN (as I have seen that some have done).  This is obviously going to be a continual issue for people IF it is related to the newer AJAX toolkit build.  Does anyone know of a fix yet or if I am doing something wrong?

I am having the same problem.  The DLL comes in two version 1.0 and 3.0, which one should I be using?