Wiki pages with same name URL broken

Strange thing: After creating many pages in the Wiki where we described different departments we also created a special wiki with all the different tasks for each department.

So we have the following for our descritpion of the backoffice department (was created first)

And just now we created the SLA page for that department:

When we now click on the toplink we go to the bottomlink and we see that page, with in the bottom the following error:

Warning: Invalid argument supplied for foreach() in /home/deb44105/domains/ on line 755

Hope you can help us soon because we run this in a production environment.