The discussion you reference fropm Peter assumes ePO of the same version on each machine, which is not your situation.
If you need to import your ePO 4.6.6. data to ePO 5.0 you have to use the compatibility (migration) tool at some point, there is no other way as the 4.6.6 data is not in a format that ePO 5.0 can work with.
if you can't get the migration tool to run then you have two options:
1. Contact McAfee support to have that investigated.
2. Build ePO 5.0 clean and set it up as if 'new' without migration.
I'm sure you know this already, but ePO 5.0 required Windows Server 2008 R2 or Windows Server 2012 and uses Sql 2008 as a minumum.