I wanted to let you know I’ve found the problem. It was exactly the same thing as the post I referenced in my original report. My client had created new content and pasted in several post titles from existing html and word documents, some of which contained a line separator character (^M or U+2028). I had exported the site content using WP’s “export” function and upon viewing the xml file with a simple unix “cat -vet” command, I saw the characters in the titles. Once I cleaned up all of the affected titles, I was able to add slides to the slideshows again.
Hopefully this can be helpful to you if it should occur again with someone else in the future.
Thanks again for your willingness to help and for producing awesome themes!
I didn’t make any changes to plugins, but my client may have made changes to the content and menus… She doesn’t have permission for anything else.
Glad I am not the only one confused :)
If there’s anything else you need me to do or want to see, let me know.
More info – tried resetting all theme options, reinstalling the theme, all to no effect. I see the same error message about avia_ajax_element as the linked post when I try to add a slideshow to a new template too. There must be something in the database causing the problem, and I have no idea how to go about finding out what it is…