I would put the javascript to be called in the behind code in your button click..
protected void btnSaveAndScheduleTask_Click(object sender, EventArgs e)
{
// do stuff.
Page.ClientScript.RegisterStartupScript(this.GetType(), "Call my function", "validatePage();", true);
}
this is how I do most of mine. Hope this helps.
And your ASP should look like..
<asp:Button ID="btnSaveAndScheduleTask" runat="server" CausesValidation="true" OnClick="btnSaveAndScheduleTask_Click" Font-Bold="true" Text="Schedule Task" />