Logging from two dlls interop

Hye.
I wanted to trace my functions by logging some informations. So i developped two dlls (.net interop) wich use log4net for logging.
when i execute one of the dlls from asp page, logging is working fine. But when i wanted to use both in the same page with "createObject("Dll1.object) and createObject("Dll2.object") i encounter problems.
The problem is a little bitte weard, all functions with the same name in these two dlls , the logs is automatically logged in the last dll instantied.
Example(c#)

Dll1 :

public void foo(){
 log.Info("Hello it's me");
}

Dll2 :

public void foo(){
 log.info("Hello it's not me!");
}

ASP page :

<%
set ob = server.createObject("Dll1.object");
set ob1 = server.createObject("Dll2.object");
ob.foo()
%>
So as result i get the log file of dll2 modified with this content :
"Hello it's not me!"
and the log file of dll1 is not modified.
And to finish, logging is working fine for the function wich has different name in these two dlls.

I don't know if i explain well, but in all cases i am sorry for my english.

Thank you in advance