several questions I have, or suggestions...
1) clear all of your cache on your browser and set it to update on every visit to the page.
2) are you using cookies for any data verification or to hold data temporarily. are you expiring your cookies properly ?
3) your "function verif()" is not doing validation on the product or message length. I submitted a message without selecting a product or typing a request.
4) your validation is checking for nulls. it is not checking if the fields were filled with spaces. are you receiving nulls or spaces ?
if you look at some of my forms validation on my site you will see I check for the length of the field and in some fields I check if it contains spaces.
http://www.getmysiteonline.com/NewAccount.asp
http://www.getmysiteonline.com/ContactUs.asp