Drop down list validation not working

Text fields are ok, but drop down list don't validate.
Using: ChronoForms_V3.1_RC5.0
What I found is the following: when I change language in .js files is that changes in JSvalidation2.php works but changes in mooValidation.js don't work.
http://www.golfclubwelschap.nl/girlzgolf/inschrijfformuliergirlzgolf

Hi Astrid,

To make a drop-down list required you must add a 'null' option at the beginning of the list e.g. <option value=''>--?--</option> otherwise the first option is takes as selected and so the 'required' criterion is met.

To change the messages simply, add them into the title attribute of the input e.g. title='Dit veld is vereist'

Bob

PS The MooValidation file is no longer used

Thx Bob!
It works now!
I us Chronoforms a lot, so changing language in .js file is easier than adding it into the form itself. But anyway: thanx for the tip.