I'm assuming it's opposite scenario that old ESA RDP plugin (version 2.5.23) is trying to connect new ESA server (2.6.12).
Please let us know what steps did you take. If my assumption is correct then the easiest solution will be to downgrade ESA core back to version 2.5.23.
I agree with Vladimir, the best way to troubleshoot this issue will be the submission of GPC case
unable to authenticate ESA Server after changing system
in ESET Products for Mobile Devices
Posted
I'm assuming it's opposite scenario that old ESA RDP plugin (version 2.5.23) is trying to connect new ESA server (2.6.12).
Please let us know what steps did you take. If my assumption is correct then the easiest solution will be to downgrade ESA core back to version 2.5.23.
I agree with Vladimir, the best way to troubleshoot this issue will be the submission of GPC case