error 503

Hi guys, I’ve installed the plugin in 3 occasions (august, early october and now with the new one) and each time I get a blank screen when I try to configure the form.
I can install it well, I go to admin.php?page=wpcf7-send-pdf to setup the form but I when I select the form the page goes white and keeps thinking, thinking and at the end I get a 503 error.
I’ve really want to use the plugin but seems to be some kind of incompability with my hosting… any idea???
Thanks!