Goals and Symptoms:

One of the requirements to upgrade ION Enterprise Server or Client system from either v5.5 or v5.6 to v6.0, is to have Service Pack 2 (SP2) of the relevant version installed prior to the upgrade. Considering that, if an ION Enterprise Server is upgraded to v6.0 before its Client(s) are applied with SP2, this will lead to a failure in upgrading the Client(s) to v6.0. Furthermore, Client(s) will not be able to work with the Server due to a version difference, hence; it¡¦ll be impossible to apply SP2 due this very same reason.

Please refer to the knowledgebase article RESL200195 for detail causes and fixes.
NOTE: Attached files can be found at the bottom of the KB article.