trouble injecting bounce message

[D. Carlos Knowlton]

The following message has appeared in my syslog every four minutes for the
past few weeks:

Sep  2 08:26:20 T1-IAS-2 qmail: 936278780.744319 warning: trouble injecting
bounce message, will try later

I am relatively new to qmail, so can anyone tell me where to begin to solve
this problem?

Thanks!

-Carlos