vCenter 8.x
The vCenter RSA agent MessageKey is controlled by a timer. After upgrading the RSA manager, the vCenter STS service has to be restarted to clear the invalid MessageKey if trying to authenticate before the timer expires to get a new MessageKey.
Restart vCenter services:
vcsa# service-control --stop --all; service-control --start --all
Or specifically the STS service:
vcsa# /usr/lib/vmware-vmon/vmon-cli --restart sts
Contact RSA support for further assistance, see vCenter RSA ready Implementation Guide.