Lightbox problem

The first thing, that the lightbox displays images too small, is something that is reported more often. It might be solved in the development version. If you want you can give it a try.

About the archive view: Make shure the option Number of images for excerpt is set to something more than 0.
If that is the case, then it seems to be that another plugin clears the images. I can’t think of another cause.

I tried the development version, it is solved the lightbox problem.

In the archive view the “Number of images for excerpt was set to 3”.

I also turned off all of my plugin except the Easy Photo Album. This is still not showing any pictures.

How can i set an other sidebar to the gallery page? Is that possible to use my theme pre defined layouts?

I think the archive view problem is caused by a function that is hooked into the_content_more_link or the_excerpt, probably by your theme. I can’t help you with that.

The same with your sidebar question, it is possible (see this support question), but you have to know your theme or ask the theme developer.