Cannot modify any forum and create new forum

Hello,

this is a very strange behaviour of UIE Forum that occured.
After upgrading to Version 5.2.3 it is not possible to modify the title, description, access control and other features of existing forums. It is even not possible to create new forums.
The only thing after clicking the "OK" -Button is that there is a blank page (with blank fields to enter title,.....)
User access for admins is set correct, so that admins have access to administer UIE Forum.

So I re-installed UIE Forum several times (with all correct steps..disbale module...deinstall it....install it...run update.php...) but the problem still exists.

Is this a error that occurs only in UIE Forum or could it be a possibility that there is an incompabitibility with other modules?

I would be very gladful if there is help available about this problem
Jakob