apt-get install stopped working

[Tom Brown <brown@esteem.com>]

When enter the command 'apt-get install ntp' I get the error: 404 Not Found 
[IP: 64.50.236.52 80]. Yet, when I use a browser to check that ip address, it 
works just fine. Furthermore, apt-get works fine on another machine behind 
the same firewall. The apt-get command just stopped working for me. Any 
ideas? Here's the full error:

tbrown@brown:~$ sudo apt-get install ntp
Reading Package Lists... Done
Building Dependency Tree... Done
Suggested packages:
  ntp-doc
Recommended packages:
  ntp-server
The following NEW packages will be installed:
  ntp
0 upgraded, 1 newly installed, 0 to remove and 0 not upgraded.
Need to get 256kB of archives.
After unpacking 479kB of additional disk space will be used.
Err http://debian.oregonstate.edu stable/main ntp 1:4.2.0a+stable-2
  404 Not Found [IP: 64.50.236.52 80]
Failed to fetch 
http://debian.oregonstate.edu/debian/pool/main/n/ntp/ntp_4.2.0a+stable-2_i386.deb  
404 Not Found [IP: 64.50.236.52 80]
E: Unable to fetch some archives, maybe run apt-get update or try with 
--fix-missing?


Thanks,
Tom