finally managed to sort out 6issue with pictures not uploading when using NextGen Gallery 2.0.66 and the WordPress SEO plugin. While images uploaded fine when uploaded through the WordPress “Add Media” option, they failed to upload to the NextGen Gallery. Upload started and at about 90% or so there was a popup letting me know that there was an unknown HTTP error and the upload failed. I narrowed it down to the WP SEO plugin. When disabled the NextGen Uploader worked just fine. So now i am using Yoast which works fine in combination with NextGen Gallery.
Because of all that hassle uploading images to the Gallery i temporarily resorted to the “Awesome Flickr Gallery” plugin and started adding images from Flickr instead of hosting them locally (which ofc was a bad decision as it increased loading time quite a bit). There also were some problems with the ColorBox script of AFG, it blocked the Colorbox script i used for images not embedded from Flickr. Clicking those images didn’t activate the ColorBox at all. Bit of a mess there and i removed that Flickr Gallery plugin and reinstalled NextGen Gallery.
As it now stands all issues with Lightbox/Colorbox are sorted, the images in the Gallery display fine and so do “regular” images in blog posts. Couldn’t be happier hehe, took me a while to figure it all out (not a WP genius in the first place) :)