Can “receive” trackbacks, but cannot “send”

Hi all,

After a fresh install of wordpress 2.2.1 on my server, it seems to be working fine, apart from the trackbacks system (I dit not check the “pinging” because I do not know yet what it is).

I created a post, http://www.leclubsante.com/wordpress/?p=1
into which I could insert a trackback comment coming from

http://www.tamba2.org.uk/wordpress/TestTrack/2007/07/18/test-leclubsantecom/

After a few minutes and after an email request for moderating this comment, it did show on my page http://www.leclubsante.com/wordpress/?p=1

But I can never do the reverse : Whichever blog I create somewhere else on another server, I can never create a post on my worpdress then add a trackback to the “outside” blog : After I enter the ping url into my post (in the field “Send trackbacks to:” ) the “ping” never shows as successful , and nothing seems to happen.

I cannot see any error in my apache / php logs.

Any clue any one ?

Any help much appreciated.