Ok, I placed the AjaxToolKit DLL in the bin directory and the installation was successful. However, when I placed Engage on my page I have received another error.
Error: Engage: Publish is currently unavailable.
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 ---