Over the last few days (I was absent before that for several months), I've been experiencing problems with the Buildings page http://en.game.industrie-tycoon.de/gebaeude.php?sort=all. When I select multiple buildings and then click a button (such as 'choose product'), I get 'page cannot be found'. I usually end up needing to 'visit' each building to make my changes one by one.
I haven't seen anyone else mention this problem, so I think it may be a situation where the game and my browser just aren't getting along. I use Maxthon 1.6.3 (build 80) Unicode. I used this same browser before my absence without any problems, but perhaps some coding on the page was changed in the interim.