I was able to install the Locator module with no problem but when I add it to the page where I want it to be displayed I get the following error:

Unhandled error loading module.
DotNetNuke.Services.Exceptions.ModuleLoadException: Unhandled Error Adding Module to BottomPane ---> DotNetNuke.Services.Exceptions.ModuleLoadException: Error: Store Locator is currently unavailable. ---> System.Web.HttpParseException: Could not load file or assembly 'AjaxControlToolkit' or one of its dependencies. The system cannot find the file specified. ---> System.Exception: Could not load file or assembly 'AjaxControlToolkit' or one of its dependencies. The system cannot find the file specified. ---> System.IO.FileNotFoundException: Could not load file or assembly 'AjaxControlToolkit' or one of its dependencies. The system cannot find the file specified. File name: 'AjaxControlToolkit' at System.Reflection.Assembly.nLoad(AssemblyName fileName, String codeBase, Evidence assemblySecurity, Assembly locationHint, StackCrawlMark& stackMark, Boolean throwOnFileNotFound, Boolean forIntrospection) at System.Reflection.Assembly.InternalLoad(AssemblyName assemblyRef, Evidence assemblySecurity, StackCrawlMark& stackMark, Boolean forIntrospection) at System.Reflection.Assembly.InternalLoad(String assemblyString, Evidence assemblySecurity, StackCrawlMark& stackMark, Boolean forIntrospection) at System.Reflection.Assembly.Load(String assemblyString) at System.Web.Configuration.CompilationSection.LoadAssembly(String assemblyName, Boolean throwOnFail) at System.Web.UI.TemplateParser.LoadAssembly(String assemblyName, Boolean throwOnFail) at System.Web.UI.MainTagNameToTypeMapper.ProcessTagNamespaceRegistrationCore(TagNamespaceRegisterEntry nsRegisterEntry) at System.Web.UI.MainTagNameToTypeMapper.ProcessTagNamespaceRegistration(TagNamespaceRegisterEntry nsRegisterEntry) at System.Web.UI.BaseTemplateParser.ProcessDirective(String directiveName, IDictionary directive) at System.Web.UI.TemplateControlParser.ProcessDirective(String directiveName, IDictionary directive) at System.Web.UI.TemplateParser.ParseStringInternal(String text, Encoding fileEncoding) --- End of inner exception stack trace --- at System.Web.UI.TemplateParser.ProcessException(Exception ex) at System.Web.UI.TemplateParser.ParseStringInternal(String text, Encoding fileEncoding) at System.Web.UI.TemplateParser.ParseString(String text, VirtualPath virtualPath, Encoding fileEncoding) --- End of inner exception stack trace --- at System.Web.UI.TemplateParser.ParseString(String text, VirtualPath virtualPath, Encoding fileEncoding) at System.Web.UI.TemplateParser.ParseFile(String physicalPath, VirtualPath virtualPath) at System.Web.UI.TemplateParser.ParseInternal() at System.Web.UI.TemplateParser.Parse() at System.Web.Compilation.BaseTemplateBuildProvider.get_CodeCompilerType() at System.Web.Compilation.BuildProvider.GetCompilerTypeFromBuildProvider(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.Compilation.BuildManager.GetVPathBuildResultWithAssert(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 DotNetNuke.UI.Skins.Skin.InjectModule(Control objPane, ModuleInfo objModule, PortalSettings PortalSettings) --- End of inner exception stack trace --- at DotNetNuke.Services.Exceptions.Exceptions.ProcessModuleLoadException(String FriendlyMessage, PortalModuleBase ctrlModule, Exception exc, Boolean DisplayErrorMessage) at DotNetNuke.Services.Exceptions.Exceptions.ProcessModuleLoadException(PortalModuleBase ctrlModule, Exception exc) at DotNetNuke.UI.Skins.Skin.InjectModule(Control objPane, ModuleInfo objModule, PortalSettings PortalSettings) --- End of inner exception stack trace ---

That did the trick!

HEY! I did one step better here!
Again, the problem for me was that we were needing to post the dll file to a hosting company where we're on a shared box and don't ahve direct access to the root bin folder without extreme hurdles to jump through.

SO, what I did was hack the module install file (sorry, no disrespect to Engage crew! just needed to get that dll installed automatically where we didnt' have bin access) so that it would upload the dll file during the normal module install in dnn.

steps:
1. add the AjaxControlToolkit.dll to the install zip (loose in there with the otehr dlls)
2. then open and edit the "engagelocator.dnn" file and add the AjaxControlToolkit.dll to the list of files it installs.

Caution:
A. of course, it helps to know what youre doing here... i only slightly do and was lucky
B. also, i already had tried the normal install and knew that the ajax dll was missing (so i was positive i wasn't overwriting one that was already there).