Hello @facil2000,
What is the version number of your copy of the plugin?
The DATEDIFF operation is included in the Date/Time operations module distributed with the Developer and Platinum version of the plugin.
Concerning to the equation you sent me as reference, the third and fourth parameters in the DATEDIFF operation are texts, so, the should be enclosed between single or double quotes, as follows:
DATEDIFF(fieldname17, fieldname15, 'dd/mm/yyyy', 'y')
Furthermore, this operation returns an object, so, if you want to know the Years, Months and Days between both dates, the correct equation would be:
(function(){
var obj = DATEDIFF(fieldname17, fieldname15, 'dd/mm/yyyy', 'y');
return obj['years']+' year(s), '+obj['months']+' month(s) and '+obj['days']+' day(s)';
})()
Best regards.