Selected index change Event in ddl is not firing

Question

Hello To All

This is my drop down list: 

<asp:DropDownList runat="server" ID="DDLCategory" AutoPostBack="true" Width="147px"

Height="17px"

onselectedindexchanged="DDLCategory_SelectedIndexChanged"></asp:DropDownList>

</div>

But Event is not firing

protected void DDLCategory_SelectedIndexChanged(object sender, EventArgs e)

{

 

// Some Code... 

} 

Please Find Out the Error 

Thanks in advance...