Validator Form Works in Firefox but doesn’t in IExplorer

I have a PHP form callinf a Validator Java Script. It works ok in Mozilla Firefox 1.5.0.9, but does in Internet Explorer 6.0.29
It doesn’t recognize any value on the form, then is complaining on the mandatory fields: so looks like Frm.elements[j].value is not valid in Intener Explorer, how I can change this script?
Thanks,