Just started seeing this on Jenkins starting with 2.8rc3. The test that triggers it writes 100 1-chunk files to GridFS using 10 threads in python. A few of the threads end up throwing this error. All writes are done with w=1 write concern.

The test code is here:
https://github.com/mongodb/mongo-python-driver/blob/v2.8/test/test_gridfs.py#L179-L194

An example of the failure in Jenkins can be seen here:
http://jenkins.bci.10gen.cc:8080/view/Python/job/mongo-python-driver-v2.8/75/extensions=with-extensions,label=linux64,mongodb_configuration=single_server,mongodb_server=master-nightly-release,python_language_version=3.2/console

I've attached the log for this failure. I can't reproduce the problem locally, just in Jenkins. But the failure is pretty consistent in Jenkins. Let me know how to help debug.