Layout change after adding an ZMS Object

Dear all,

after adding a new ZMS object (myZMStheme20), the layout of all our 
websites hosted changed (for an example see www.3nasen.com). the old 
layout is displayed for half a second and then disappears to some rough 
layout. I think it must be something in the stylesheet - but where to 
change - and why did that happen after adding a ZMS object?

Thanks for your help,
stefan