Import project to Gitlab.com failed

In my Gitlab CE 13.6.1, I exported my project to tar.gz file (Settings->General->Advanced->Export Project).

Than I tried to import it into new project of Gitlab.com EE 13.7.0-pre. (new project->Import project->Gitllab export). It run for 10 seconds & show “Internal server error” without other details.

Whats wrong?