Once a decent amount of data (20GB in our case) is added to mongo db, creating an index causes the following error message to be output to the log many times:

[DataFileSync] FlushViewOfFile failed 33 file

There doesn't seem to be any data corruption, so I don't know if this is an issue with the actual flushing operation, or if the message gets erroneously logged.
More info in the group thead:

https://groups.google.com/forum/#!topic/mongodb-user/B2wFJEgYYPo

Could possibly be a dupe of SERVER-1163