What does the `kernel: WARNING: at net/sched/sch_generic.c dev_watchdog()` error indicate?

Issue

• System loses network connectivity, network driver backtraces found in /var/log/messages similar to the following:

WARNING: at net/sched/sch_generic.c:... dev_watchdog+0x.../0x...() (Not tainted)
Hardware name: ...
NETDEV WATCHDOG: ethX (<drivername>): transmit queue N timed out
Modules linked in: ...
Pid: ..., comm: ... Not tainted 2.6.32-....el6.x86_64 #1
Call Trace:
<IRQ>  [<ffffffff........>] ? warn_slowpath_common+...
[<ffffffff........>] ? warn_slowpath_fmt+...
[<ffffffff........>] ? dev_watchdog+...
[<ffffffff........>] ? run_timer_softirq+...
...
[<ffffffff........>] ? __do_softirq+...
...
[<ffffffff........>] ? call_softirq+...
[<ffffffff........>] ? do_softirq+...
[<ffffffff........>] ? irq_exit+...
...
<EOI>  [<ffffffff........>] ? ...
...