1. i have problem for two scriptmanager while click update button..
You cannot have two scriptmanagers on a page. Only one.
2. Issue in code:
ScriptManager.RegisterStartupScript(myPage, this.GetType(), "showalert", "alert('" + Message + "...!!');", true);
ScriptManager.RegisterStartupScript(this.Page, this.GetType(), "showalert", "FixHeader();", true);
I see you have given same name to two scripts. This simply means you copy-pasted it and have no idea what parameters are for RegisterStartupScript. Bad.
'
showalert
' -> have different names.