There is currently an issue on German environments only that the login dialog of Vault inside the "Aufgabenplaner" - task scheduler doens´t appear on the German version of Inventor 2013.
We are currently working on a Solution for that.
We detected that the issue occurs only inside a x64 OS.
If you want to the migration either wait until we have a fix or find a machine with a Win XP x86 or Win7 x86 OS and run the migration from there.
Update: a Hotfix is provided and will solve the issue: Fixedfor_DTM13_1532
Update2: this hotfix is not part of SP1 of Vault 2013!