Is this security vulnerability or any attack by hacker?

I've written error handler onto my site which send me a mail when error occurs.  I have hosted my site on shared hosting.

I often get this message:

P3NWVPWEB006 Error in:http://mysiteadd.com/WebResource.axd?d=HkZ2Th6FgWcJHtFBAL4AoLIIVV9LZGXpbV Error Message: This is an invalid webresource request.

at System.Web.Handlers.AssemblyResourceLoader.System.Web.IHttpHandler.ProcessRequest(HttpContext context) at System.Web.HttpApplication.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously)


Inner Exception: This is an invalid webresource request.
Target Site: System.Web.IHttpHandler.ProcessRequest
App Domain Name: Name:/LM/W3SVC/1040/ROOT-1-130349668026365409 There are no context policies.
Exception Type: System.Web.HttpException
Envt Stack Trace: at System.Environment.GetStackTrace(Exception e, Boolean needFileInfo) at System.Environment.get_StackTrace() at CommonClass.SendMail(Exception i_oErr, String ClientIp) at ASP.global_asax.Application_Error(Object sender, EventArgs e) at System.Web.HttpApplication.RaiseOnError() at System.Web.HttpApplication.RecordError(Exception error) at System.Web.HttpApplication.PipelineStepManager.ResumeSteps(Exception error) at System.Web.HttpApplication.BeginProcessRequestNotification(HttpContext context, AsyncCallback cb) at System.Web.HttpRuntime.ProcessRequestNotificationPrivate(IIS7WorkerRequest wr, HttpContext context) at System.Web.Hosting.PipelineRuntime.ProcessRequestNotificationHelper(IntPtr managedHttpContext, IntPtr nativeRequestContext, IntPtr moduleData, Int32 flags) at System.Web.Hosting.PipelineRuntime.ProcessRequestNotification(IntPtr managedHttpContext, IntPtr nativeRequestContext, IntPtr moduleData, Int32 flags) at System.Web.Hosting.UnsafeIISMethods.MgdIndicateCompletion(IntPtr pHandler, RequestNotificationStatus& notificationStatus) at System.Web.Hosting.PipelineRuntime.ProcessRequestNotificationHelper(IntPtr managedHttpContext, IntPtr nativeRequestContext, IntPtr moduleData, Int32 flags) at System.Web.Hosting.PipelineRuntime.ProcessRequestNotification(IntPtr managedHttpContext, IntPtr nativeRequestContext, IntPtr moduleData, Int32 flags)

Why I'm getting this message.?