I figured something out.. in de js file of the validator is the next section:
formatAndAdd: function( element, rule ) { var message = this.defaultMessage( element, rule.method ), theregex = /\$?\{(\d+)\}/g; if ( typeof message == "function" ) { //message = message.call(this, rule.parameters, element); >> original line message = jQuery.format(message.replace(theregex, '{$1}'), rule.parameters); // replaced line } else if (theregex.test(message)) { message = jQuery.format(message.replace(theregex, '{$1}'), rule.parameters); } this.errorList.push({ message: message, element: element }); The first time the field is validated the script goes to the "else if", the second time you focus/blur the field the first rule of the "if" kikck in and returns "the filname" or "[object][OBJECT]"... So I replaced the first "if" with the same statement as the "else if " and it seems to work fine now. I know this is not a neat solution, and i also don't know why it works now as it does... if you know a better solution, please let me know!