it is now ??
I used most of the day trying to fix it.
after reading up about php, phpBB and so on i was still blank.
Since i have been working with wp for a year now, i have a descent controll over which files you find where, so i started looking through the folders.
After some time i found that wp-united had createt a sub-folder in the content-folder where it placed a file i did not reconize. So i deleted that, and everything worked! puh!
I am taking a backup of my whole installation now, and shall upgrade to 2.9.1 later this evening, then fix the sidebars and so on…