title: Sudden and unreproducable 'A potentially dangerous Request.Path value'
body: <p>Yesterday for about 2 minutes the error log for my site has this error message:</p>
  
  <pre><code>A potentially dangerous Request.Path value was detected from the client (?).
  </code></pre>
  
  <p>for 7 different errors relating to these two queries:</p>
  
  <pre><code>/flash/userImage.ashx?id=53210cd9-2e34-4b27-9315-28c3525cb15c&amp;type=micrositePhoto&amp;width=750
  /flash/userImage.ashx?id=53210cd9-2e34-4b27-9315-28c3525cb15c
  </code></pre>
  
  <p>I am unable to produce this error by typing the URL into my website.</p>
  
  <p>This is the stack trace:</p>
  
  <pre><code>at System.Web.HttpRequest.ValidateInputIfRequiredByConfig()
  at System.Web.HttpApplication.ValidateRequestExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute()
  at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean&amp; completedSynchronously)
  </code></pre>
  
  <p>It seems to be something internal to asp.net/IIS.</p>
  
  <p>What could have caused this error? Is it some hack attack? I don't understand why it complained about the path then, when subsequent queries are fine. In my error log function, I am getting the pageURL like this:</p>
  
  <pre><code>pageURL = HttpContext.Current.Request.Url.ToString();
  </code></pre>
  
  <p>I log the following information about errors: the pageUrl, the error message, the stack trace, the error date, and the user logged in, if there is one. Is there something else I should log to help me debug this? I can't think of anything.</p>