I can't seem to find anything about this error on the Internet. I've checked the AJAX source code and just can't seem to find any hint as to what is causing this to happen.
If I clean the browsing cache, restart the server, the first thing I get is this error, when I refresh, the error goes away and the AJAX controls cease to work. If a restart the server, reopen the browser without clearing the cache it seems to work...
Here's the stack-trace of the error which occurs when it tries to initialise the ToolkitScriptManager:
[FormatException: String was not recognized as a valid DateTime.] System.DateTimeParse.Parse(String s, DateTimeFormatInfo dtfi, DateTimeStyles styles) +3211050 System.DateTime.Parse(String s, IFormatProvider provider) +28 System.Windows.Forms.TypeLibraryTimeStampAttribute..ctor(String timestamp) +38 System.Reflection.CustomAttribute._CreateCaObject(RuntimeModule pModule, IRuntimeMethodInfo pCtor, Byte** ppBlob, Byte* pEndBlob, Int32* pcNamedArgs) +0 System.Reflection.CustomAttribute.CreateCaObject(RuntimeModule module, IRuntimeMethodInfo ctor, IntPtr& blob, IntPtr blobEnd, Int32& namedArgs) +46 System.Reflection.CustomAttribute.GetCustomAttributes(RuntimeModule decoratedModule, Int32 decoratedMetadataToken, Int32 pcaCount, RuntimeType attributeFilterType, Boolean mustBeInheritable, IList derivedAttributes, Boolean isDecoratedTargetSecurityTransparent) +529 System.Reflection.CustomAttribute.GetCustomAttributes(RuntimeAssembly assembly, RuntimeType caType) +103 System.Reflection.RuntimeAssembly.GetCustomAttributes(Boolean inherit) +33 System.Web.UI.AssemblyCache.GetAjaxFrameworkAssemblyAttribute(Assembly assembly) +76 System.Web.UI.ScriptManager.get_DefaultAjaxFrameworkAssembly() +388 System.Web.UI.ScriptManager..ctor() +26 ASP.login_aspx.__BuildControlToolkitScriptManager1() +33 ASP.login_aspx._BuildControl_control4(Control __ctrl) +127 System.Web.UI.CompiledTemplateBuilder.InstantiateIn(Control container) +12 System.Web.UI.MasterPage.InstantiateInContentPlaceHolder(Control contentPlaceHolder, ITemplate template) +87 ASP.site_master.__BuildControlcontent_body() +120 ASP.site_master.__BuildControlform1() +111 ASP.site_master.__BuildControlTree(site_master __ctrl) +179 ASP.site_master.FrameworkInitialize() +22 System.Web.UI.UserControl.InitializeAsUserControlInternal() +35 System.Web.UI.MasterPage.CreateMaster(TemplateControl owner, HttpContext context, VirtualPath masterPageFile, IDictionary contentTemplateCollection) +8832342 System.Web.UI.Page.get_Master() +54 System.Web.UI.Page.ApplyMasterPage() +15 System.Web.UI.Page.PerformPreInit() +45 System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +328
The page uses an AutoCompleteExtender but the page doesn't even get far enough to load the rest of the controls. I've been banging my head against a hard wall for ages to figure it out.