There are bugs in Domino Administrator Client 6.01. Please refer link below :
http://www-1.ibm.com/support/docview.wss?rs=203&q=1095364&uid=swg21095364&loc=en_US&cs=utf-8&lang=en+en
Btw, you can use Domino Administrator Client 5.x but you can not use the policy feature.
By my experience, I have a problem too to migrate personal folder using nupgrade.exe. Sometimes nupgrade.exe will be generated a NSD File and the migration process failed.