Don't change the server.xml. Instead use the ServiceBindingManager to start multiple instances of the server on the same machine. See this for details http://community.jboss.org/wiki/AS5ServiceBindingManager
thanks jaikiran pai.
I modified all the ports in the D:\jboss-126.96.36.19900721-M4-Server1\server\default\conf\bindingservice.beans\META-INF\bindings-jboss-beans.xml file.
Only this server, I left all default ports on the second server.
I did not read everything on that link you pointed me to, it's a bit long and i'm a bit in a hurry, i hope that i did not miss anything important.
Basically it seems ports configuration no longer occurs in server.xml file but in bindings-jboss-beans.xml file.
Someone correct me if i am wrong.
I should add one thing :
the topic of my problem is not correct.
Indeed I am not using 2 instances of a single server but 2 instances that come from 2 servers.
One instance, one server.
I know one can run multiple instances of a single server, so i believe that precision is important.