Ok,

I have found the issue.

There was some function with wrong syntax.
This syntax was no problem in version 5.01 in my report
Code:
wrong 
     let bausblenden = false
     if ({KstDaten.storno} <> 'E') then
         let bausblenden= true
     end
     return( bausblenden or ({?Kurzuebersicht}<>1) )


right
     return((bausblenden = true) or ({?Kurzuebersicht}<>1) )
or
     return(({KstDaten.storno} <> 'E') or ({?Kurzuebersicht}<>1) )
But I did not realize that this was another file. All version parameters were the same.
After the replacement, the preview went to the designer and the faulty function was displayed.

If you guys have a problem after publishing a version, a little note in the forum and the
hint where to find a small bugfix is enough.