Paula & Max, the options with “Post/page images only…” activate some javascript that tries to detect if image links belong to the same post or page before attaching the FancyBox routine to them and grouping them in Galleries. This will make a difference for example on a category page or the front page where you have multiple posts listed. When you use the option “all images, one gallery” and you would click an image from the first post then you will be able to flip forward to other images from other posts listed on that page. The other options prevent that.
The fact that the other two options do not work for you, is because that javascript is looking for <div class="hentry">...</div>
to determine to which post/page an image belongs. A lot of WP themes live by that convention but both your themes do not place post/page content in a div with that class.
The next release of Easy FancyBox will have an option to make it compatible with your theme. In fact, you can try the development version right now: https://downloads.www.ads-software.com/plugin/easy-fancybox.zip It has this feature already along with a new “Spotlight” effect when opening images…
Paula, if you decide to try it, set the new option “Group selector(s)” to “div.postarea”. Max Engel, in your case it’s “div.post” that should do the trick. Then you can try different variations of the two new options above it, controlling the FancyBox enabling and gallery mode ??