Default website security will block certain text that it thinks might be a hacking attack.
You may inadvertently triggert this of you use < or > or any unusual characters in the text you submit.
Details:
System.Web.HttpException (0x80004005): A potentially dangerous Request.Path value was detected from the client (:).
at System.Web.HttpRequest.ValidateInputIfRequiredByConfig()
at System.Web.HttpApplication.PipelineStepManager.ValidateHelper(HttpContext context)