Management summary: nothing to worry
What you spotted is not an error, but an error status shown in debug mode. You should only activate Debug(ns:driver) when modifying the driver source code, or when you are in deep trouble.
The error code 11 stands for EAGAIN on Linux system and means "there is no data available right now, but you might try again later". It is quite common that web clients terminate their connections ungracefully (e.g. users not waiting for a page to be loaded completely, and clicking on the next page).
