Compared php, javascript and eXist db files on FrancoToile and Lansdowne video sites. Eventually discovered that the code I'd written to replace Mike's id() calls included some explicit calls to the TEI namespace which had not been declared. This caused eXist to return an error. We have fixed the problem in helpers/get_events.php, but I'll have to go through all the other instances of id() and my replacement code to ensure they're properly written, either with the namespace declaration and namespace prefix, or with neither. Thanks to Martin for spotting the problem, see his post.

Not yet sure if it will also solve the problem with the Map of London site reported here.