It should say 1024...It looks as though you have either a loss of 24 megs or it is being shared by something.
Remove the 2nd stick of ram...reboot and navigate back to the properties page and see what it says then.
Then swap them around and try it and see what is reported. You will be able to tell which is shorted that way if it is loss if it is shared then there should be a 24 meg difference on each stick singly checked.
You can also download this freebie and it will give you more details as to what you have installed. see what it says...It could be a windows error...