With the scheduled server/site outages today, I've seen a couple of WUs error out. Those were due to problems downloading the files that are a part of the WU. I'm presuming it's just a timing matter where the servers went down before your machine could finish the download and it timed out. You'll notice that the sent time and return time are rather close to the same in your Results Status like this:

R00323_ c5c4a1cc9a1b3704f4f6694ea5c98eb3_ 00_ 14--  Amberscomputer Error  7/7/09 21:26:03 7/7/09 21:27:24 0.00 0.0 / 0.0 
HFCC_ t1_ 01091503_ TrkB_ 0001_ 0--  Amberscomputer Error  7/7/09 21:25:45 7/7/09 21:27:24 0.00 0.0 / 0.0

If you click on the Error link, you'll see something like this:

<core_client_version>6.6.36</core_client_version>
<![CDATA[
<message>
WU download error: couldn't get input files:
<file_xfer_error>
<file_name>batch00323_R00323_c5c4a1cc9a1b3704f4f6694ea5c98eb3.sequence</file_name>
<error_code>-224</error_code>
<error_message>file not found</error_message>
</file_xfer_error>
<file_xfer_error>
<file_name>batch00323_R00323_c5c4a1cc9a1b3704f4f6694ea5c98eb3.dist.gzb</file_name>
<error_code>-224</error_code>
<error_message>file not found</error_message></file_xfer_error>

</message>
]]>

I've since gotten new WUs successfully. After the recent CEP problems, din't want to see folks freaking over this.