it seems that the previous support message was not quite correct, but unfortunately in the meantime, i've attempted to follow the instructions at http://codex.wordpress.org/Moving_WordPress
(the site seems to be working okay in the new folder but now i can't login to WP at the old address.)
anyway, i'm going to persist with uk2 in case i need duplicator again at a later date. i'll let them know about extending the php time out, but meanwhile, here's there latest response, which might mean something to you ...
Thank you for your reply. I do apologize for the inconvenience and confusion on this matter. You can install any WordPress plugin that you wish. The only requirement is that it is up to date. If not, it may not work correctly.
It appears that the Duplicator plugin is using Zend Optimizer and an outdated version of IonCube. They seem to be using modules from PHP 5.2.x. It needs to be updated so it is compatible with PHP 5.3.x. Also, I would recommend you verify that your WordPress installation and all its plugins are up to date. Once that is done, you can try installing the Duplicator plugin again. If you still experience problems, we may be able to assist you further, however, in order to do that we will need you to provide us the login details to the admin area of you WordPress installation. This will allow us to re-create the error while monitoring our error logs to pin point the exact error.