 <p>Your id is null when you submit the form that's why you are getting this error.</p> <p>Either specify the the id parameter nullable as you have done in the get method or </p> <p>store the id in a hidden field to pass it automatically with the model like this</p> <pre><code>@HTML.HiddenFor(Model.id) </code></pre> <p>or pass it manually</p> <pre><code>@HTML.Hidden("id",id) </code></pre>