"Permission Denied" using CallBacks from an MTS Component

Hi,

I'm trying to make an application that have's a reference to a DCOM object, running in a Transaction Server.
My client side application must pass, to the DCOM component, a reference to itself, so that he (the MTS component) can make a callbak to a function on the client side.
My problem appears when I try to make this CallBack, the error message "Permission Denied" always appears.

I tried to set up correctly de DCOM configurations, using dcomcnfg.exe on the client side, but the problem still persists.

If anyone can help me.....
Thanks in advanced.