Error reading request entity data

[ashishwave]

We have a mail server in our DMZ running sendmail and its webmail
interface "openwebmail" (from openwebmail.org) . openwebmail works
using perl cgi scripts on apache.
Now, the problem is that most of the times, whenever a person
logs in to the openwebmail from outside (from internet )using linux
based PCs (browser: konqueror, firefox) THEN most of the times (but
not all times) this error appears in httpd.log of the apache server
[Sat Mar 21 19:28:45 2009] [error] [client 59.180.19.19] (70007)
The timeout specified has expired: Error reading request entity data,
referer: https://........

When a person uses Windows based PCs (using firefox, IE) then this
problem is very rare, (but is not completely ruled out too).

When a person accesses the webmail interface from inside (DMZ or
LAN) then this problem never occurs.

There was no change in our DMZ architecture, mail server, apache
configuration etc for last one year, although this problem has
occurred since last six months only.

note: We searched on google and found that "The timeout specified has
expired: Error reading request entity data, referer" error message in
apache's error log is a known problem, but there was no pointer to the
solution.

Kindly give any pointers for the solution of the problem.

bye :-)
Ashish Ranjan