I FOUND THE SOLUTION: PLEASE DELETE THIS MESSAGE!
The builtplate of my 1 week old Ultimaker2 won't raise properly. It only raises about 8 cm, then stops.
Everything worked just fine yesterday.
Today I wanted to fine tune the builtplate, and started the procedure. When the builtplate was raised to begin with, it stopped short by about 2 cm from the nozzle (when it asked me to adjust it to 1 mm from the nozzle, which evidently wasn't possible).
After that I raised the builtplate by going to the Advanced settings. It then stopped even further down. And subsequent attempts only made it worse. Now it will only raise about 8 cm.
I uploaded new default firmware from within Cura. I turned the machine off and on. Nothing helped.
I tried to print stuff, but as it started to print mid air, I aborted the printing.
What is wrong? What to do?