@xinot: Apart from the fact I really have bad experiences with Realtek NIC's...have a look at your NIC's energy saving settings (not only the Windows Power settings, but the NIC settings in devicemanager=> advanced), to make sure the NIC isn't just going to sleep.
No power saving options enabled in this PC (Windows power saving options disabled + manually disabled all via device manager, USB, NIC, etc.). Only monitor can go to sleep...
SharePort seems to use multiple UDP ports as i see from W7 Resource Monitor.
4 ports all the time open and 2 extra when connecting/disconnecting to device. If i read this correctly...
Have to keep this resource info on eye if there happens something when this error come again.