Thank you very much Rohit Gupta, That worked.

Except the lightbox popup does not display the image, will look in to that.

viewimage.php had the same engine/start.php in it, so replaced:

require_once(dirname(dirname(dirname(__FILE__))) . "/engine/start.php");

with this:

$autoload_root = dirname(__DIR__);
 if (!is_file("$autoload_root/vendor/autoload.php")) {
 $autoload_root = dirname($autoload_root);
 } 
require_once "$autoload_root/vendor/autoload.php";
 \Elgg\Application::start();

Thanks  Rohit Gupta, That also worked.

Now the lightbox popup does display the image.

Had also to tweak the size of the images to display right in the lightbox.

I am glad that it worked.

I think the problem is that the code of the Time Theme Pro plugin (probably based on the Time Theme from the same developer) wasn't completely and correctly updated to take into account the changes necessary to work on Elgg 2. One thing that probably causes the error is that Elgg JS code is no longer loaded in the page header but loaded asyncronously as AMD modules. Plugins should do it the same way. And in case a plugin relies on any Elgg core JS it will cause errors as the loading order is not necessarily the same if you don't define dependencies correctly.

Maybe someone can suggest a working alternative theme to you (unfortunately I can't as I have written my own theme for personal use based on the default Aalborg theme and never really tried any others on Elgg 2).

Or you might have to think about hiring a developer if you need a theme with specific features and a look you like but don't find one you like.

ok thank you man

@RvR where's the docs that explain how to make a plugin please ? 

http://learn.elgg.org/en/stable/tutorials/hello_world.html