Hi! I'm having a nervous breakdown!
I have problems with my widgets making the following error:
"Not Found Sorry, but you are looking for something that isn't here."

http://www.gtechinvest.com/wordpress/aktien/

What's very peculiar is, that on pages where the default widgets are on, everything runs as it should!

... Anyone?!

I am using:
Atahualpa theme 3.7.3
WP 3.3.1
Super Post & Page Widget 0.4e
Dynamic Widgets 1.5.0

Hello again,
I cas see that you quite often suggest us to inactivate plugins to find out what happens then... And so I did.
My problem was Super Post and Post Widget - not working correctly with WP 3.3.1 Instead I installed Page in Widget and it looks like it's working just fine (even if this Plugin hasn't been verified with WP 3.3.1 either, but at least compatible up to 3.2.1).

Thanks for the update Snaaran. Good troubleshooting.