when Say can not update mac os x?

First, ensure that you have a complete disk backup or two, possibly made to an external disk using a tool such as Disk Utility. If something is wrong here, this backup may be the only path to recover your data.

As for the update, OS X 10.6.8 is the end of the 10.6 series. If you're having trouble with an update, then download and install the 10.6.8 combo update manually. Here are the OS X Server 10.6.8 combo, and OS X client 10.6.8 combo update kits. (While this is the OS X Server forum, I'm going to guess that you're probably really running 10.6.8 client.) See if that combo installation works.

If you really need 10.6.7, then try downloading the combo update for that, and see if that installs.

If the 10.6.8 combo update fails, please post which Mac is this, and whether there any errors logged in the Console.app around the failing update. (Applications > Utilities > Console.app) Also post what might have happened here, if you know of anything that might possibly have effected the updates; hardware problems, disk errors, disk corruptions, etc.