Error: "Specified argument was out of the range of valid values" when populating dynamic DropDownLists
<p>I added two DropDownList controls programatically. When the first DropDownList's index is changed the second DropDownList should get populated. The first DropDown gets populated on Page Load.</p>

<p>When I select an item from the first DropDown, a DataTable is filled with values that need to be populated in the second DropDown. On setting the breakpoint I found that DataTable is filling properly.</p>

<p>But when it reaches line:</p>

<pre><code>ddl.DataSource = dt;
</code></pre>

<p>it gives error:</p>

<pre><code>Specified argument was out of the range of valid values
</code></pre>

<p>I also found that ddl is picking the right DropDown.</p>

<p>The problem I find is that while postback some error is happening.</p>

<p>I tried even doing:</p>

<pre><code>dd.Items.Add("abcd");
</code></pre>
