[OpenAFS] rx failed to send packet

[Stephen Joyce]

Hello,

I have a server which runs several scripts with AFS tokens. These scripts 
often manipulate PTS users and groups and less-often perform volume 
operations.

For the past ~week, I occasionally see in the output the following message.

  "rx failed to send packet: rx_sendmsg: Operation not permitted"

I've checked and the operations that are being performed at the time the 
message is seen appear to have been carried out successfully.

The only google hit I find for this exact message is in the following 
presentation, and I don't think there's enough info in the slide to 
determine underlying cause. <https://agenda.infn.it/materialDisplay.py?contribId=10&materialId=slides&confId=5625>

Before I go diving deep into my scripts and activate all of the debugging, 
can anyone point me towards a possible cause and/or solution to that 
message?

Client is running openafs 1.6.1-1+ubuntu0.3. AFS db servers are running 
openafs 1.6.1-1+ubuntu0.2. KDCs are running a scarily-ancient Heimdal.

Cheers,
Stephen