Thank you very much for that howto everything seemed to work since I got to the part where the *.vdmk Disk needs to be convertet.
The Zip File I got (app.vagrantup.com/rapid7/boxes/met...) contains 10 Disks files. Disk 1 (Name: disk-s001.vmdk) is about 3,5 Gb and I tried to convert that.