Hello guys!

My first post here after working with drupal now for three years. That really means that I'm kind of desperate ;-)
Well what's going on? Simply:

I've installed a website for a customer. Everything is very basic. I've only added a custom type. Everything worked while testing it as admin-user. Now I've created an other account for this website and this user is not able to edit, add, ... stuff on the website.
While I was debugging I found out that the global $user remains unset. Even if I log in with the admin account the output of following code is empty:

global $user; dsm($user);

The part that freaks me out is that I'm still able to edit/add content as the admin user. If I'm not using the admin account but the regular user account (with almost same permissions) I receive the following error:

PDOException: SQLSTATE[23000]: Integrity constraint violation: 1048 Column 'uid' cannot be null: INSERT INTO {entity_translation} (entity_type, entity_id, language, source, uid, status, translate, created, changed) VALUES (:db_insert_placeholder_0, :db_insert_placeholder_1, :db_insert_placeholder_2, :db_insert_placeholder_3, :db_insert_placeholder_4, :db_insert_placeholder_5, :db_insert_placeholder_6, :db_insert_placeholder_7, :db_insert_placeholder_8); Array ( [:db_insert_placeholder_0] => node [:db_insert_placeholder_1] => 18 [:db_insert_placeholder_2] => en [:db_insert_placeholder_3] => [:db_insert_placeholder_4] => [:db_insert_placeholder_5] => 1 [:db_insert_placeholder_6] => 0 [:db_insert_placeholder_7] => 1361871397 [:db_insert_placeholder_8] => 1361871397 )

Sounds logic to me. There is no uid found in the global $user.

What is going on here? Anyone any clue?