My Express (use as extended wifi) lose connection with Time Capsule

[fa.ce]

Hi,
i use Lion, last version.
I've setup my wifi network and use Time Capsule (3rd gen) as master and Airport Express (4rd gen) as extended wifi.
Everything goes well for 1 or 2 days but suddenly AE lose connectivity and disappear from Utility Airport (though green led is on).
I've to turn off Airport Express or reset and relink to Time Capsule.
Any hints ?
Thanks

 

[Kashika]

Have you turned on the settings in Airport Utility to let the TC's network be extended?

Is your AE in bridge mode?

 

[fa.ce]

Yes to first question.
Second: not sure about that, how to verify it ?
I remember that i've had some problem settings the TC as bridge.

I've read somewhere (not remember well) that Lion has some problem with network wireless, is it correct ?