Take a look at
http://bugs.digium.com/view.php?id=7351
Might be related. I've seen this too.
There's a (very simple) patch attached which you can try.
-----Original Message-----
From: users-bounces(a)openser.org [mailto:users-bounces@openser.org] On
Behalf Of David Coulthart
Sent: Wednesday, May 30, 2007 10:49 AM
To: users(a)openser.org
Subject: [Users] Malformed CANCEL request from Asterisk possibly
impactingOpenSER?
We are currently experiencing problems with our production OpenSER
(1.1.0) environment where the load on the server is steadily increasing
and the OpenSER response time increases drastically (e.g., 30+ seconds
for an internal call to ring).