Can anyone see a problem with this validation script?

It seemed to be working fine but now only works up until the address has been entered. Once you get to the card payment part - the form can be sent half done.

function validateForm(form)
{ 
var Card_ExpMon = form.Card_ExpMon.value;
var expyr = form.Card_ExpYear.value;
var temp = new Date();
var nowMonth  = temp.getMonth();
nowMonth ++;
var nowYear = temp.getFullYear(); 
var Card_CardType = form.Card_CardType.value;
var emailID = form.Customer_Email.value;
//alert(Card_ExpMon);
//alert(expyr);
//alert(nowMonth);
//alert(nowYear);
//alert(Card_CardType);

	if (form.Customer_Name.value == "")
	{ 
	   alert("Please Enter First Name."); 
	   form.Customer_Name.focus( ); 
	   return false; 
	}
	else if (form.Customer_Surname.value == "")
	{ 
	   alert("Please Enter Your Surname."); 
	   form.Customer_Surname.focus( ); 
	   return false; 
	}
	else if (form.Customer_Address1.value == "")
	{ 
	   alert("Please Enter Your Address."); 
	   form.Customer_Address1.focus( ); 
	   return false; 
	}
	else if (form.Customer_Town.value == "")
	{ 
	   alert("Please Enter Your Town."); 
	   form.Customer_Town.focus( ); 
	   return false; 
	}
	else if (form.Customer_County.value == "")
	{ 
	   alert("Please Enter Your County."); 
	   form.Customer_County.focus( ); 
	   return false; 
	}
	else if (form.Customer_Postcode.value == "")
	{ 
	   alert("Please Enter Your Postcode."); 
	   form.Customer_Postcode.focus( ); 
	   return false; 
	}
	else if ((form.Customer_Email.value==null)||(form.Customer_Email.value=="")){
		alert("Please Enter your Email address")
		form.Customer_Email.focus()
		return false
	}
	else if (echeck(form.Customer_Email.value)==false){
		form.Customer_Email.value=""
		form.Customer_Email.focus()
		return false
	}

	else if (form.Customer_Tel.value == "")
	{ 
	   alert("Please Enter Your Telephone Number."); 
	   form.Customer_Tel.focus( ); 
	   return false; 
	}
	else if (form.Card_Country.value == "-")
	{ 
	   alert("Please Enter Your Country."); 
	   form.Card_Country.focus( ); 
	   return false; 
	}
	else if (form.Card_CardType.value == "-")
	{ 
	   alert("Please Enter Your Card Type."); 
	   form.Card_CardType.focus( ); 
	   return false; 
	}
	else if (form.Card_Nameoncard.value == "")
	{ 
	   alert("Please Enter Name on Card.");
	   form.Card_Nameoncard.focus( ); 
	   return false; 
	}
	else if (form.Card_Cardno.value == "")
	{ 
	   alert("Please Enter Card Number."); 
	   form.Card_Cardno.focus( ); 
	   return false; 
	}
	else if (isNaN(form.Card_Cardno.value))
	{ 
	   alert("Card Number must be a valid number."); 
	   form.Card_Cardno.focus( ); 
	   return false; 
	}
	else if (form.Card_Cardno.value.length < 16)
	{ 
	   alert("Please Enter Valid Card Number with no spaces."); 
	   form.Card_Cardno.focus( ); 
	   return false; 
	}
	
	//perform verification on issue dates and verification number depending on card type
	switch(form.Card_CardType.value) { 
		case 'Switch': 
			if ((form.Card_IssueMon.value == "-" ) || (form.Card_IssueMon.value == ""))
			   {
			   //alert(form.Card_Verifyno.value);
			   alert("Enter the month your card was issued."); 
			   form.Card_IssueMon.focus( ); 
			   return false;
			   }
			else if ((form.Card_IssueYear.value == "-" ) || (form.Card_IssueYear.value == ""))
			   {
			   //alert(form.Card_Verifyno.value);
			   alert("Enter the year your card was issued."); 
			   form.Card_IssueYear.focus( ); 
			   return false;
			   }		
	    break;

		case 'MasterCard': 
	    break;
		
		case 'VisaCard': 
		break;
	}		
	if ((nowYear > expyr) || ((nowYear == expyr ) && (nowMonth > Card_ExpMon)))
	{ 
	   alert("Expiry Date has expired."); 
	   form.Card_ExpMon.focus( ); 
	   return false; 
	}
	else if (form.Card_Verifyno.value == "")
   {
	   //alert(form.Card_Verifyno.value);
	   alert("Please enter your verification number."); 
	   form.Card_Verifyno.focus( ); 
	   return false;
   }
	else if (isNaN(form.Card_Verifyno.value))
	   { 
	   alert("Your verification Number must be a valid number."); 
	   form.Card_Verifyno.focus( ); 
	   return false; 
	   }
	else if (form.Card_Verifyno.value.length != 3)
	{ 
	   alert("Your verification Number must be 3 digits."); 
	   form.Card_Verifyno.focus( ); 
	   return false; 
	}  
	else if (form.Customer_Tel.value == "")
	{ 
	   alert("Please Enter Your Telephone Number."); 
	   form.Customer_Tel.focus( ); 
	   return false; 
	}
}

//email validation function, called from within above validateForm function
function echeck(str) {

		var at="@"
		var dot="."
		var lat=str.indexOf(at)
		var lstr=str.length
		var ldot=str.indexOf(dot)
		if (str.indexOf(at)==-1){
		   alert("The E-mail that you have entered is not valid")
		   return false
		}

		if (str.indexOf(at)==-1 || str.indexOf(at)==0 || str.indexOf(at)==lstr){
		   alert("The E-mail that you have entered is not valid")
		   return false
		}

		if (str.indexOf(dot)==-1 || str.indexOf(dot)==0 || str.indexOf(dot)==lstr){
		    alert("The E-mail that you have entered is not valid")
		    return false
		}

		 if (str.indexOf(at,(lat+1))!=-1){
		    alert("The E-mail that you have entered is not valid")
		    return false
		 }

		 if (str.substring(lat-1,lat)==dot || str.substring(lat+1,lat+2)==dot){
		    alert("The E-mail that you have entered is not valid")
		    return false
		 }

		 if (str.indexOf(dot,(lat+2))==-1){
		    alert("The E-mail that you have entered is not valid")
		    return false
		 }
		
		 if (str.indexOf(" ")!=-1){
		    alert("The E-mail that you have entered is not valid")
		    return false
		 }

 		 return true					
	}

As I was looking through your code... and getting a splitting headache.... I thought why would you be creating your own code for this?

Use an AJAX library like JQuery with a validation plugin. Here is a link (not to my site) that will make this process very simple.

http://docs.jquery.com/Plugins/Validation

Not what you were asking for, but effective.