Object reference not set to an instance of an object error message
<p>What is wrong with my code? I recently posted a question about <a href="http://stackoverflow.com/questions/11754489/calculation-in-code-behind">Calculation in code behind</a> and I tried Vinoth's answer but it gives me an error at this line:</p>

<pre><code>bool isChaffeurUsed = (bool)Session["IsChaffeurUsed"];
</code></pre>

<p>error message is: <strong>Object reference not set to an instance of an object.</strong></p>

<p>Please tell me what should i do. Many thanks and have a nice day.</p>
