The system failed to flush data to the transaction log. Corruption may occur.
This message is logged by the NTFS driver, indicating that a write request was not completed successfully.
The message itself does, unfortunately, not indicate on which drive the error occurred - if there are multiple drives connected to the system.
I have seen this message logged when an external USB HD would temporarily disconnect (due to a hardware issue).
This message is also logged when a USB device (e.g. memory stick) is disconnected without being properly ejected first.