Load Test Reference error step is not defined

I build serval truclient scripts for firefox with VuGen Version 12.01. During a load test started from HP ALM 12.01 i get an error for several virtual users:

ReferenceError: step is not defined
undefined
While calling handlers in RuleEngine dispatch, event=[Event type="step/ready-state-updated" target="16: Wait for switch left image"], handler=
addOnetimeEventListener: type=step/ready-state-updated, function=function (e) {
"use strict";

var retVal = true;
var step = e.target;
if (step.readyState._aborted) {
retVal = false;
delete step.readyState._aborted;
}
else if (step.readyState.isReady) {
if (step.type == "handler" && !step.preemptive) // Do not allow other handlers to interfere?
disableHandlers = true;

After this error message the user process is still running but the script itselfs stopped. Does anyone has an idea, it is quite urgent.

// Note - when calling the state setter the step is pushed into the Step.STATE_* array
step.state = Step.STATE_RUNNING;
step.run.callAsync(step);
} else {
var timeout = RTS("step/readyTimeout", step);
if (timeout === undefined || (new Date()).getTime() - step.startTime <= timeout * 1000) {
retVal = false;
}
else {
// Note - when calling the state setter the step is pushed into the Step.STATE_* array
step.state = Step.STATE_RUNNING;

if (Script.state == Step.STATE_STOPPING)
step.end(Step.RETCODE_ABORTED_SUCCEEDED, {
extRetInfo : Step.EXT_RET_INFO_STOPPING
});
else
step.onReadyTimeout();
}
}
Event.dispatch("step/processed", step, { retVal : retVal});
} [MsgId: MERR-205177]