adClosed callback is defined in the mbrixVars. It should be the name of function defined elsewhere.
There is no adVerification callback defined
adInstance should be a string with no whitespace
mrixVars.adVerification = "verifyFlex"
mbVars.adClosed = "onCloseAD"

function verifyFlex(status){
     if(status === 1){

     }else if(status ===0){
          //No ad is available. 
     }
}

function verifyFlex(status){
     if(status === 1){
          //Ad is avaible
          setTimeout(function () {
           
        }, 1000);
     }else if(status ===0){
          //No ad is available.
          onCloseFlex();
     }
}

function onCloseFlex(){
     var swf = getSwf();
     FR.util.log('Media Brix AD UNIT: ', ad_unit);

     try {
          swf.enableGBSound();
     } catch (e) {
          //do nothing
     }   


}