I've been seeing a few DP's reporting failure to process one or more packages.

Go to the DistMgr log and you can see it is refering to an invalid system name.

Why? Well, some environments might have reused sitecode but change the server name.

These systems predate me. What is odd is a system from 5 years ago (yes that long ago) appeared in a distmgr log file this week, anyway to solve this check out this great posting on the ConfigMgr support teams blog which does a great job on pointing out the steps needed to clean this up:

Packages may try to access a Distribution Point that was removedimage

If you take a look at all the calls we get here in the SMS/ConfigMgr support group, this one would have to rank right up there in popularity.  What happens here is the Distribution Point (DP) share, or the DP itself, is removed but you still have packages pointing to the missing resource. 

Usually you'll know this is what happened because the distmgr.log shows something like the following:

Cannot establish connection to
["Display=\\<server>\<share>\"]MSWNET:["SMS_SITE=<site>"]\\<server>\<share>\ SMS_DISTRIBUTION_M
ANAGER 17672 (0x4508)

Error occurred. SMS_DISTRIBUTION_MANAGER 17672 (0x4508)

Read more here: http://blogs.technet.com/configurationmgr/archive/2009/02/25/packages-may-try-to-access-a-distribution-point-that-was-removed.aspx