Incremental migration

Hi,

I am trying to do a migration as described here: https://wiki.zextras.com/wiki/ZxBackup:_Incremental_migration_with_ZeXtras_Backup
In step 3 I am doing the single domain export.

I can import the data on the new server without problems. However, going back to step 3 (as suggested in step 7) using the same command and same export directory gives me a 'directory not empty'.
So, it looks like incremental migration is not possible when using single domain method?
Or am I doing something wrong?

Sietse