Like Cory says it's a problem with Xinet's Appleshare server. Install the patch as soon as you can.

Here's what Apple says about it:

Information Regarding Issues With Xinet Server
INSTRUCTIONS: If creative professional customers enquire about the Xinet server and
Mac OS X, the following statement should be used. If you have customers that use Xinet
server products, this notice can be used to let them know that Xinet will be providing an
update to improve the reliability of their product. We should at all times encourage
customers to evaluate and deploy Mac OS X Server, Xserve and Xserve RAID for high
performance, scalable networked file storage.

A small number of customers have encountered an issue when using the Xinet FullPress
file server with Mac OS X clients. This issue is evidently specific to the Xinet server
product and is related to how Xinet incorrectly manages unique file identifiers on servers
with massive numbers of files under heavy activity loads. The Apple File Protocol (AFP)
requires the use of "persistent file IDs." These file IDs have always been supported by
Mac OS X Server and most third-party AFP-compatible file servers, and Apple has
provided detailed engineering support to Xinet to conform to this long-standing
specification.

Xinet reports that they have diagnosed the issue and will provide an update to improve
the reliability of FullPress under heavy server activity that triggers this issue.

Creative professional customers have many options for their server-side production
needs. Mac OS X Server is a great AFP server and running on the Xserve G5 and Xserve
RAID, it provides a robust, powerful, and scalable solution for managing up to 3.5
terabytes of high-performance networked storage.

Part Number: L301947A-US
Release Date: Jan 29, 2004