I have a textbox which i convert to tinymce textbox using tinymce.js file. I'm trying to add a new script with database fields substituted based on selection made from dropdownlist to page using registerstartupscript.

In page load

protected sub page_load(byVal sender as object, byval e as EventArgs) handles me.load
    AddScriptToPage()
    if not page.ispostback() then
        session("fname") = nothing
    end if
end sub

Script Method

Sub AddScriptToPage()
            dim _script = " c.onRenderMenu.add(function(c, m) {  " & _
                    add_columns() & _
            "});  "
    ClientScript.RegisterStartupScript(Me.GetType(), keyword,_script)        
End Sub

function add_columns() as string
    dim ret_string = String.empty
    select case ddlList.selectedvalue
        case 1
            sqlcommand = "xyz"
        case 2
            sqlcommand = "xyz"
        case 3 //Load from excel
            sqlcommand = nothing
    end select
    if sqlcommand isnot nothing then
        executereader()
        while reader.read()
            ret_string  = ret_string & reader("column") 
        end while
    elseif session("fname") isnot nothing   
        dt = getdatatable(session("fname").tostring()) //method that opens oledb connection and returns columns
        for each dr in dt.rows
            ret_string  = ret_string & dr("column") 
        next
    end if
 add_columns = ret_string
end function

When excel file is uploaded to server this event is called

protected sub btnclick(byVal sender as object, byval e as EventArgs) 
    if hasfile then 'i have custom properties set after control validation
        'Upload file
        'set session value with filepath
        session("fname") = filepath
        'call js register event
        AddScriptToPage()
    end if
      end sub

When i click upload button i'm calling AddScriptToPage, and debug it it hits AddScripttoPage event and executes it but it doesn't showup on page. It should show column names in tinymce editor but it doesn't. But when i click another button on the same page it shows (becos session has the filename).

On Upload button click page flow:

1. Page load - AddScriptToPage is executed (registers scripts with no columns)
2. Then AddScriptToPage in btnclick event is executed (registers scripts with columns)

Why is this script not getting registered even though it is executed on vb code on uploadclick event? And why does it show up after another button click and not original button click that calls this event?