Newbie needs help getting data from client to server

[aspiring geek]

I'm using a callback (ICallbackEventHandler) to retrieve data from
client and process on server.

Original VB code was (on page load):
btn.Attributes("OnClick") =
Page.ClientScript.GetCallbackEventReference(Me, _
"document.all.item('Spreadsheet1').csvdata", "MyCallBack",
"null", "MyErrCallBack", True)

Rendered:
<button id="btn"
OnClick="WebForm_DoCallback('__Page',document.all.item('Spreadsheet1').csvdata,MyCallBack,null,MyErrCallBack,true)">Submit
Data</button>

Runtime error occurred
line: 118
Error: Cannot use parentheses when calling a Sub

I understand what the error means, but not how to fix it. I can't add a
"Call" before the sub, and I can't remove the parens. Any
ideas/suggestions?

I'm also open to another way to get the
'document.all.item('Spreadsheet1').csvdata' --client-side visible
control's data-- back to the server. I haven't been able to get the
client side controls recognized in VB back code, and can't recognize
server controls (asp textbox for example) in client page code, so I was
trying the only way I found that gets data to the server without using
a server control. I haven't been able to get Session to work either.