Core Issue
The system ran out of buffer elements, which are used to queue items. One common reason for this error message is an error in the async interrupt software, when modem control or flow control interrupts are occuring at a high rate - typically more than 1000 interrupts per second. One cause of a high rate of interrupts might be due to a loose or faulty cable attached to the console, aux, or other async line of the router. Another would be to connect a non-async device - such as a KVM switch - to an async port.
Resolution
Identify the faulty device or cable attached to the router, and disconnect or replace it. If you can't identify a faulty or misbehaving device, copy the error message exactly as it appears on the console or in the system log. Consider upgrading to software with the fix for CSCsx68596, or CSCtf45737, depending on your router model. If you cannot determine the nature of the error from the error message text or from the show buffers command output, call your Cisco technical support representative and provide the representative with the gathered information.