c# store Array collection

Well. here is the scenario.
to make my life easier for now.
I have a webmethod. submits from the client side first. Then the server side fires off from a button
OnClick="btn_submit_Click"  OnClientClick="Validate();"
so I am trying to retrieve the data hold after the client side submits and reuse it on the server as the postback starts

On the client side but need to hold it to pass it to the server side.

I try it. but I get
Object reference not set to an instance of an object.

  [WebMethod(EnableSession = true)]
        [ScriptMethod]
        public static string SubmitInfo(ies[] iesSe)
        {

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here is my array that is submmited from the client side alreay. if I could hold iesSe when the serverside is running.
Remember everything is running altogether. There is no stop or pause the client side run then the server side right after.

thanks guys. these were great solutions. I decided to just convert it all to angularjs using a webmethod. thanks again.