Code being stripped out of form tag

Hi

Some of my client pages have forms in it. They include javascript checking of the form and the javascript is included in the fck editor for that page.

To activate the form checking I add

onsubmit="return FormCheck(this);"

into the form tag.

I save the document and check and the code is still there.

But it is appearing on all forms that when someone uses a form the next time the

onsubmit="return FormCheck(this);"

gets stripped our of the form tag.

I am guessing this is a fck editor issue?

Looking forward to ANY ideas as the client has about 16 forms on his site and daily checking them is not good !

Example
https://www.peopleaid.org/sponsorarickshaw_20.html

Thanks

Chris