Number of physical memory pages belonging to (user) memory client that have been selected for retirement exceeds threshold.
The number of unreliable physical memory pages belonging to (user) memory client has exceeded the threshold.
See the event description for more detailed information specific to this event. Further information on memory page retirement can be found in the VMware KB articles Percentage of host memory was retired (2008220) and ESXi host firmware reports too many corrected errors in some parts of the system memory (2002020).
Refer to the VMware Online Documentation for more information on vCenter event messages and possible solutions.