go to device manager, check the power manangment setting on the 82567lm ethernet card. Check and see if allow the computer to turn off this device to save power is checked. if not check it.
The only problem that this setting is absent in 14.6 and 14.7 and NIC goes to 10Mbps and (sometimes) does not return from low power state.
However, this option is present in driver version 10.5.1.0 from Microsoft and works as expected.
YOu can also try this:
Error: E6400 systems Ethernet card disconnects after LCD screen turns off
Solution: Run Regedit.exe. Click on computer. From menu select edit/find. Search for SipsEnabled Change from 1 to 0. Press F3 to search for next until all are changed. Reboot
This is a known "Feature" with the intel driver, took us a long time to figure this feature out and change it so it would not disconnect & change the speed of the network connection.
Did you ever get this issue resolved? i have seen similar posts, but the only resolution I've seen is to not place the system in sleep/standby