Unknown server tag 'cc1:CalendarExtender'.

This is due to ajax version.put the correct version..

Embedded statement cannot be a declaration or labeled statement

http://msdn.microsoft.com/en-us/library/xaw06638(VS.80).aspx

Sys.InvalidOperationException: ScriptLoader.loadScripts cannot be called while the ScriptLoader is already loading scripts.

Solved..put this script

<script type="text/javascript" language="javascript">
var prm=Sys.WebForms.PageRequestManager.getInstance();
prm.add_initializeRequest(initializeRequest);

function initializeRequest(sender,args){
if(prm.get_isInAsyncPostBack())
args.set_cancel(true);
}
</script>