If the range extender has an aerial that you can reposition, try it so that the aerial is transmitting on the same plane. By that I mean, with my AP downstairs and my M1001 upstairs, moving the aerial so that is was nearer the horizontal greatly improved signal strength and stability.
I had problems with an M1001 when it had low signal strength. It generally failed to get a dhcp address.
Out of interest, have you tried setting your M1001 to use a fixed IP address ? I wonder what the dhcp lease time is ?