I'm so near yet so far to getting my customised version of the Slideshow block to work

I'm actually only going to use it with filesets - not arbitrary files.

Here's the problem:

Add MySlideshow helper (is that the term?) comes up correctly, with the filesets in place

I click on 'Add' button with url javascript:$('#ccm-form-submit-button').get(0).click()

I can see that the block has been added

The helper doesn't close and animation continues until i have to close the browser tab to get out of it