In Mac OS X Server v10.6, the Software Update service may not be able to download the catalog or update files from Apple’s public Software Update servers if your server is behind a HTTP proxy.
If your server is behind a HTTP proxy server and Server Admin does not list any available updates, check the /var/log/swupd/swupd_syncd.log for the following messages:

server.example.com swupd_syncd[31893] <Info>: ========== Sync Started ==========
server.example.com swupd_syncd[31893] <Error>: Unable to retrieve catalog(s) from the Apple server
server.example.com swupd_syncd[31893] <Info>: Sync Complete

If network access is interrupted, a Mac OS X v10.6 client may not be able to reconnect to an Active Directory domain whose name ends in ".local".

In Mac OS X Server v10.6 or Mac OS X v10.6 client, the computer may become unresponsive and display a spinning cursor if the computer is bound to an LDAP server using SSL.
This may occur whether the LDAP server is a Mac OS X Server Open Directory server or a third-party LDAP server.
The option to use SSL is available in Directory Utility on the client computer. It is not enabled by default, but may be enabled by users or administrators to increase the security of directory binding.

Software Update may not be able to find updates when using a cascaded Software Update Service in Mac OS X Server v10.6. One of these alerts may appear on client computers:

The Software Update Server (server.example.com) is not responding.
 
The file "index-leopard.merged-1.sucatalog" couldn’t be found on the server "server.example.com".

Certain alerts reported in Mac OS X  Server v10.6′s caldav error.log are expected in certain circumstances, as described below.