The first image appears, doesn't open in the lightbox. The second image appears for 2 seconds, then disappears and also doesn't open in the lightbox. What did I do wrong?
For the JavaScript not rendered into your page: Please switch off the JavaScript Optimization in the Plugins configuration. If you don't have this option, please update your plugin.
This option HAS to be switched off, if your blog is cashing the entries, and normally it is switched off by default.
Cashing in global is a problem for dynamic plugins like the Lightbox plugin. The code for entries is only created once. So if you change the type of the script used to produce the effect, the script is changed but the entry still has old informations. So your choices here are to switch off the entry cashing (plugin extended article attributes) or recash all entries after changing the script style.
On my site Lightbox 1 and Graybox is not working, too, and never did. I think, there was an error in the plugin before, that I was not interested to fix yet, because the ThickBox script was the most convenience type for me, looking the best and supporting the best close mechanisms.