I though it was an incompatibility between my router (Zyxel) ant the AE n. It is not the case. Not the router acts as a mere PPPoE modem and the AE n manages everything else... Still, after 2 days of use with apparently no problems, it reseted.

It especially happened during my use of the N800 and in certain conditions:

Use of skype N800 version
FLV (Flash 9) videos