After successfull install no access to any admin-functions

Today i try to install the new G3 system on my server. After uploading and decrompressing the ZIP on my server, i open the URL http://mydomain.de/gallery3/...

I got an setup assistent who say that i must create a folder named "var" with 777 permissions... OK, i do that, checking again and getting the go for the next step. I insert the informations for my DB ( i create for the first time a new db to looking around a bit with the new version). After filling the files i click on the button to reach the next level...

The installer say to me, I'm ready (Wow... that was fast) and open again my directory on the server who i placed my new version. On the frist time i got an window who remember me on a thickbox effect... I see the same content again in this window like the page in the background... OK, i close this "internal popup" and see the gallery page. Now i insert the informations for the admin access who i got from the installation and i see some administration menus... But on each step who i will doing around the administration (including uploading pics), i got this message from the server...

Dang... Something went wrong!
We tried really hard, but it's broken.
Talk to your Gallery administrator for help fixing this!

After this message i was logged out from my profile.. I can repat this every time, i got the same message again and again. I also try to install the G3 again with a cleared dbase, but same results...

What's wrong with my installation? And I'm wondering me that someone telling here, that the have a way to import the old dbase from Gallery 2... I didn't see any message who asking me that in the installation-process. I can only fill in the informations for my db access, nothing more...

Informations about my server: