Big Excel Interop Problem - Master requested

[Arch4ngel]

I have an ASP.NET that require authentication.

Here is some details :
-Virtual Directory Created (lets call it VD)
-IIS disabled Anonymous access to that VD and enable Basic Auth with a existing and working Domain.
-Activated the Integreated Auth on the application VD
-Application use Excel Interop
-DCOMCNFG have already been configured on the server (configuration is okay... unless you think I might be wrong there)
-Same version of excel is on both machine (mine and server) Excel v10.0.6501.0 which correspond to Office XP with SP3

Here is the problem :

[color=#0000ff]private[/color] Excel.Application m_app;
[color=#0000ff]private[/color] Excel.Workbooks m_wbs;
m_app = [color=#0000ff]new[/color] Excel.ApplicationClass();
m_wbs = m_app.Workbooks;

The three first line work perfectly but the last one launch an exception :
QueryInterface for interface Excel._Application failed.

[font=Arial, Helvetica, Geneva, SunSans-Regular, sans-serif]Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: System.InvalidCastException: QueryInterface for interface Excel._Application failed.
[/font]
The problem however doesnt occure on the developpement machine. It only occure on the server. I dont have direct access to that server so I must call a system admin each time to modify something in it.

Please.... help ? Somebody have already seen this error ? Somebody know how to solve it ?

N.B.: Im currently using C# to make all my code but I can make a traduction to VB.NET anytime.

Thank you very much