When rebooting the prompts to enter setup, then select save and exit.
This is not really an error. The configuration of some systems means new memory must be updated in the CMOS.

This can be caused by a few issues.

1. You have reached the systems maximum memory and it will not recognise anymore above its limit.
2. The system does not recognise the chip type of the memory module. If the new memory is single sided, it requires double sided. If the memory is double sided, it requires single sided or the system is unable to use that size capacity module.

Assuming you have found the right memory socket (check manual), then the memory is incompatible.
If the module is too long or short - the wrong type of module has been ordered or shipped (for example SDRAM instead of DDR).
If the memory notches do not line up - then the wrong voltage of memory has been ordered or shipped.

Assuming you know what the new memory amount should be (existing memory plus new memory amount), your operating system has an option to display total memory available.

Windows
Right mouse-click on the "My Computer" icon and select "Properties." The total memory is displayed under the "General" tab.

Mac
Click "About This Mac" or "About This Computer" from the Apple menu or Apple symbol in the top left corner of your Desktop. Total memory amount should be displayed.