function OnCheckLogon(form)
{
	var usename = form.username.value;
	//alert(usename);
  		if ((usename=="")||(usename+""=="undefined"))
		{
			alert("用户名不能为空！")
			form.username.focus();
			return false
		}
	var password = form.password.value;
	//alert(usename);
  		if ((password=="")||(password+""=="undefined"))
		{
			alert("密码不能为空！")
			form.password.focus();
			return false
		}
		
	var imgnumber = form.imgnumber.value;
	//alert(usename);
  		if ((imgnumber=="")||(imgnumber+""=="undefined"))
		{
			alert("验证码有误！")
			form.imgnumber.focus();
			return false
		}

	document.body.style.cursor='wait'; //显示沙漏

   return true;
}