Hi,
We have looked into this and there doesn't appear to be a way to make it work. The root of the problem is ajax:ComboBox can't be placed inside an absolute positioned element. To see the problem, you can try the following code:
Code: HTML/ASPX
<div style="position:absolute;left:10px;top:200px;">
<ajax:ComboBox ID="ComboBox2" runat="server">
<asp:ListItem Text="Zero" Value="0" />
<asp:ListItem Text="One" Value="1" />
<asp:ListItem Text="Two" Value="2" />
</ajax:ComboBox>
</div>
If you try the above code and open the drop down, you will notice that the drop down is displayed at the wrong position. This is because the AJAX ComboBox failed to account the parent DIV position. In some cases, the drop down box will be completely out of the view due to this location error. This is the case for the CustomColumn for the Grid. Unfortunately there is no way that we can make the ajax:ComboBox to adjust for the parent element position. So there doesn't appear to be anyway to make it work. Sorry about it!
Thanks!