[problem with print size]

I own the Anycubic i3 MEGA and it is defined in Cura 3.4.1 with the correct settings.

 

But i´m NOT able to slice a part with 210x210 mm (wich is my print size).

I sent it to a frind with Simplfy3D, he sliced it for me and now its printing.

Any idea why this happens? I disabled skirt, brim and so on.