This problem is related to 6.0.x machine keys only. Some changes to EEPC 6.1 were required in order for it to work with ePO 4.6, this involved how the machine key was stored.
Providing you use the new version of EETech supplied with EEPC 6.1, it will deal with this problem.
This problem has been fix in 6.1.1.
Also note that when your clients are upgraded from EEPC 6.0.x to EEPC 6.1.0, it will automatically send a new machine key and recovery information to ePO. This is implemented in the 6.1 RTW build.
Sorry for any inconvenience
Thank you VERY much for the quick and accurate response!