Server Tag not well formed with ASP:CheckBox

I have read through the various topics and found none that assisted me in my situation.

Based on whether the checkbox is checked I will pass in the name of the checkbox and reference id#.

I did the following but I am getting a server tag not well formed error when were calling the "OrderCheckedChanged" method and if i change the quotes to "" than the string SP turns into a variable. Please advise.

 <asp:CheckBox ID="chkSP" runat="server" Checked='<%#Eval("sp")%>' onclick='<%# String.Format("OrderCheckedChanged('SP',{0});", Eval("reference_order_id"))%>' ToolTip="Specialty Product" Enabled='<%# IIf(Eval("order_type").ToString = "Invoice" Or Eval("gp_order_id") = 0, "False", "True") %>' />