Ajax refresh

Im trying to refresh a placeholder from a WEBBlock layout.When i do that i get this error i dont know why:

Object reference not set to an instance of an object. 
Not sure what the problem might be.
Can you give a simple espace where it occurs?
Hi Filipe,

It would be nice if you could give more details about your issue.
However I think you're trying to access some element that is not available on the HTML in the execution moment.
Do you got any javascript errors on your browser console?
And why are you trying to refresh a placeholder and not its content (you can for example enclose all the content with a container and refresh that div)?
Hope this helps but I needed more information(eSpace, error logs, etc..) about your issue to help you with more details.

Best Regards,
Gonçalo M.