There is an issue where different blocks include the same jquery plugins under different path/file names, The consequence is that a jquery plugin can be included twice, hence jquery.fn.plugin_name gets declared twice and the second declaration breaks jQuery.
(if you look in the developer console log you will see an appropriate error message)

To confuse it further, sometimes a plugin is patched into a file with a name nothing like that of the plugin (like view.js) because that was the only way for an add-on to get it to load at the time.

I got caught out on that a few months back. The popup login block includes fancybox within view.js, and the sortable fancybox gallery also includes it. Hence a jQuery duplicate declaration.

The solution is to hack the code to delete fancybox from one or the other blocks (or both and load it in the template, which is what I did).

There was some discussion on integrating a solution for this into C5, but has gone quiet lately with the push on 5.5. I don't know what the current status is.

Thanks again John, will have ago but failing that I'll have to look at something else, maybe add jquery normally as I would outside c5.

Cheers once again though.

Had the same issue, Extracted following code from view.js (of pop_up login box) and disabled it and place the code in header/footer.php of your theme.

$(document).ready(function() {
$(".login-popup-link").fancybox({
'titlePosition': 'inside',
'transitionIn': 'none',
'transitionOut': 'none'
});
});

Thanks very much Jordan, you are right, I did install it in the blocks folder I'll now change it and have a go.

Much appreciated, have a good day :-)

Works a treat, thanks again Jordan