This message indicates that the network interface encountered an access time-out from the CPU's main memory. There is probably nothing wrong except system overload.
If the system is busy with other processes, this error can occur frequently. If possible, try to reduce the system load by quitting applications or killing some processes.
The Lance Ethernet chip timed out while trying to acquire the bus for a DVMA transfer. Most network applications wait for a transfer to occur, so generally no data gets lost. However, data transfer might fail after too many time-outs.
For more information about the Lance Ethernet chip, see the le(7D) man page.