Periodically_call_remote doesn´t work properly

Hi everyone:
I have some problems using periodically_call_remote, here is my code:

<%=periodically_call_remote(:url => ‘http://localhost:3000’, :frequency
=> ‘0.5’, :update => {:success=>‘imagen’})%>

<%=image_tag("/guarrada/Debug/foto.jpg") %>

My problem is that when I load the web page, it works properly for 3 or
4 refresh, but after that I have the result of the attachment image.
Ayone can say me what I´m doing wrong??