Cannot find free page...

[David Christian <dchristian@macalester.edu>]

I am transferring a lot of data between a proprietary OS and a linux
Intranet server daily.  When I get over a certain limit for an individual
transfer, it gives me this message:
Cannot find free page......
eth0: memory squeeze, deferring packet
eth0: memory squeeze, deferring packet

(repeat for screen after screen full)

The data manages to get across, so my question is: is there a way I can
avoid this message?  What exactly is causing it?