HTML-PHP form not working well other than FF

[iosoft]

I have created an admission form which is NOT working very well with other than Firefox. Thats is, problem with IE5.5, IE6 and even with Chrome.

The problem is with the JAVASCRIPT codes. IE firing "ERROR ON PAGE" :huh:
Not with PHP codes.

This is my test page -
Apply Online
JS: http://ghz.t35.com/validation.js
Please help me to solve these stupid problem. Its mission critical for me.

 

[JeDiKnight]

very clearly the page isn't getting the isdate() function correctly...please check that this function is accessible...