multiple calls to scripts with onSubmit

Hello,
I am not very knowledgeable about javascripts, but I have a problem, I need
to run a basic form checking script on several pages, but as I am already
running 2 scripts when I submit the form I dont know if I can also run a
third?
at the moment my line reads:
<form action="<%=MM_editAction%>" method="post"
enctype="multipart/form-data" name="form1"
onSubmit="checkFileUpload(this,'GIF,JPG,JPEG,BMP,P NG',false,'','','','','','
','');return document.MM_returnValue">

This works splendidly, however as I said I also need to ensure that certain
form fields are filled in!
How can I call a third script ? If I try adding :

onSubmit="checkFileUpload(this,'GIF,JPG,JPEG,BMP,P NG',false,'','','','','','
','');MM_validateForm('LastName','','R','FirstName ','','R','CustomerEmail','
','R','BillingAddress','','R','BillingCity','','R' ,'BillingStateOrProvince',
'','R','BillingPostalCode','',
'R','BillingCountry','','R','BillingPhoneNumber',' ','R','ShipLastName','','R
','ShipFirstName','','R','ShipAddress','','R','Shi pCity','','R','ShipStateOr
Province','','R','ShipPostalCode','','R','Statemen tAccepted','','R');return
document.MM_returnValue">

The last script, the form checker wont run at all? (Ps the script form
checking the form works well if I remove the call to one of the other 2
scripts) So it doesnt seem to want to run more than 2 scripts via onSubmit!

Please help,
Joe