 <p>Is there a reason you were using <code>Request.Form</code>? You should use</p> <pre><code>Guid myGuid = Guid.Parse(GuidToken.Value); </code></pre> <p>If you still want to use Request.Form which I would not recommend, the name of the hidden field control has been changed by asp.net so the collection does not contain exactly what you specified because it has some autogenerated naming convention added to it. It now looks like this</p> <pre><code>Request.Form["ctl00$MainContent$GuidToken"] </code></pre> <p>Debug mode</p> <p><img src="https://i.stack.imgur.com/1ywh4.png" alt="enter image description here"></p>