Yes, that's why I wrote "solved the issue for me. The image overlay works now as it should and it displays the current image number only which is what I wanted". I should have added it can be left blank too as intended but with the double quotation marks inside the single ones.
I wanted to only display the image number, but nothing is cool too =)

Weird you couldn't replicate the issue. I got an error during validation and the image opened as a regular link, no overlay or thumbnails. =(