I have “Server Error in '/' Application. Invalid postback or callback argument.” and i dont know how to fix it

Question

I have a WebForm page which contains a link to a User control. This user control has a grid view with a button. When I push the button it invokes a pop up dialogue (another user control) that requests user information.

When i click submit i get a server error 'invalid post back...' I have other pages like this one, but they work perfectly fine. do you have any idea what could be wrong?

note that may be helpful: the text boxes do contain validation, that don't let you pick a weight less than 0. or leave a field empty. could it be this?

thankyou for your help guys

 <asp:GridView  ID="GridView1" class="GridMain" AutoGenerateColumns="False" RowStyle-Wrap="true"  DataKeyNames="ID_MSG_SLIP, ID_ITEMPER_COLLECTIONORDER, ID_COLLECTIONORDER" runat="server">
    <Columns  >
        <asp:TemplateField HeaderText="Confirm Collection" ItemStyle-VerticalAlign="Middle" ItemStyle-HorizontalAlign="Center" >
            <ItemTemplate>
                <asp:ImageButton ID="btnGreen" runat="server" Class="btnGreen" ImageUrl="~/img/green.png" CommandArgument='<%#Eval("ID_MSG_SLIP")+","+ Eval("ID_ITEMPER_COLLECTIONORDER")+","+ Eval("ID_COLLECTIONORDER")%>'/>
                <!--This is the pop up panel and trigger   -->
                <pop2:DatePopUp ID_MSG_SLIP='<%#Eval("ID_MSG_SLIP")%>'  ID_ITEMPER_COLLECTIONORDER='<%# Eval("ID_ITEMPER_COLLECTIONORDER")%>' ID_COLLECTIONORDER='<%# Eval("ID_COLLECTIONORDER")%>' runat="server" ID="DatePopUp" />

Answer 1

    if(!isPostBack){
//Load your grid data inside this
}