signalR - Error during WebSocket handshake: Unexpected response code: 500

Having recently started playing with signalR, I got the following error:

WebSocket connection to 'ws://localhost/../signalr/connect?transport=webSockets&clientProtocol=1.4&connectionToken=DJquvX4%2B7kH0EzXZcCYSRPL66R3ytyc204DflljN1%2BgkHqi6Y5llDAAeUZTDKkDFFBQm6rdJooh8ck7LcejXVFZvhxE0iUJVD%2BZadN%2Ff5s13rc%2FMZD4WxsMSlToyvYid&connectionData=%5B%7B%22name%22%3A%22myapp%22%7D%5D&tid=4' failed: Error during WebSocket handshake: Unexpected response code: 500

This was odd as it was working fine on another development machine I was using. After serious amounts of hunting around and mucking about, I got it working by adding the following to the web.config:

<system.web>
    <httpRuntime targetFramework="4.5"/>
</system.web>

Interestingly, I found the answer in the Application Event Logs :)

It's also worth checking that the application target framework is also set to 4.5 in case there is a conflict there too.