ComboBox - ComboBox1There was an error rendering the control.

Hello,

I am using the ComboBox from the Ajax Toolkit in VS2013. However I get the following error:

ComboBox - ComboBox1

There was an error rendering the control. Value cannot be null. Parameter name: Stream

When I try running it the dropdown appears outside of the textbox. Can anyone tell me what the problem is. Trioed changing the Render mode to Block , but this does not resolve the issue. Call ComboBox definition below:   

<cc1:ComboBoxID="ComboBox1"runat="server"OnSelectedIndexChanged="ComboBox1_SelectedIndexChanged2"RenderMode="Block"style="position:absolute"></cc1:ComboBox>

regards

Pat