 <p>I encountered this error when trying to debug to run a web application after publishing from VS 2012 to IIS 7.5. After some hair pulling, I realised that the problem was the fact that I did not change the jquery script and signalr paths when deploying.</p> <p>To solve the issue I had to add the virtual directory name ("TestingChat") to the path of the script tags for jquery and signalr.</p> <p>E.g. From this: </p> <pre><code>&lt;script src="Scripts/jquery-1.8.2.min.js" &gt;&lt;/script&gt; &lt;script src="/signalr/hubs"&gt;&lt;/script&gt; </code></pre> <p>To </p> <pre><code>&lt;script src="/TestingChat/Scripts/jquery-1.8.2.min.js" &gt;&lt;/script&gt; &lt;script src="TestingChat/signalr/hubs"&gt;&lt;/script&gt; </code></pre>