I use the Package Management to Add or Remove packages.
After click Update, the following error windows appears:
Packages Not Found
bold text
And list all the packages could not be found on my system.
This error occur when I try to add and remove many packages. When I add a few packages that require only one installation CD, it is OK.
Pls help me to solve this problem!

How many cd disks did you use to install Fedora origionally?

I assume that you checked off the packages that you wanted to add, then clicked update?

Take a look at this article about adding packages to Fedora and see if it helps.