When attempting to upgrade Backup & Replication from 5.0.0 to 6.0.0, an error occurs stating you need at least version 5.0.1 to upgrade.
To perform upgrade of Veeam Backup & Replication to version 6.0.0, you must be running version 5.0.1 or 5.0.2
Please see the licensing Article for further information related to your product and upgrading.
http://www.veeam.com/kb_articles.html/KB1191
http://www.veeam.com/kb_articles.html/KB1217