It’s a real nightmare to release a new version of NextGEN Gallery. One the one hand new features , on the other hand every upgrade should run smooth… If you a one-man-show this could causes a real headache. I’m really did my best for each and every upgrade, but it’s impossible for an installation base of 50.000 – 100.000 blogs. With Version 1.8.0 I modify the permalink structure of the gallery links, which is for the future more SEO friendly (I really hate SEO optimisation)… but I missed to test some custom structures (i.e.
/%category%/%postname%/ ). So the new feature will break the plugin for this structures. Sorry, for any trouble this caused. I’m looking into this and hope to fix it in a couple of weeks…
In the meantime you have three options :
a) Stay on Version 1.7.3, which should be fine (download here)
b) Change your permalink structure ( Could be a SEO issue )
c) Deactivate just the Gallery permalinks (See gallery settings)
Update : Should be fix with Version 1.8.3