CMOS memory size mismatch
Memory has recently been added or removed from computer
It is normal for a computer to report a memory size mismatch or memory error when memory has been added or removed from the computer. When this error is encountered, enter CMOS and ensure the settings for the memory are properly set and then save and exit from CMOS.
Memory settings improperly set in CMOS
It is possible for CMOS to become corrupt or for the memory settings to be set back to default. Enter the computer CMOS Setup and ensure that the CMOS memory settings are properly set for the amount of memory you have in the computer.
Issue with computer memory or motherboard
If the CMOS settings are properly set for the amount of memory you have in the computer and the issue persists, it is possible that a memory confliction with incompatible memory may be present. If memory has been recently added to the computer, remove that memory to see if the issue resolves itself.