you got this error above the preview window right?
try to refrest the page and see if it is still there in yes
Show me plese your script - what have you added or changed before this appeared.
The errors above preview can be eather reason in bad internet connection or too much cookies in the browiser and sometimes thay do not have anything to do with script.
But sometimes the script hs right codind but the sombination of it causesx error - for example regarding wrongly done looping animation and it is not able to process it.