Thank you very much for your answer !
Now it runs, but i've detected 2 problems :
1 - my 6600 can't read correct MIME TYPE on IIS, so it do not understand the response type and make an error.
I've move my Test page to an Apache server
2 - 6600 and 3650 don't have the same Download Descriptor MIME Type :
3650 => text/vnd.oma.dd
6600 => application/vnd.oma.dd+xml
So I've made 2 directory with different mime type (defined into an htaccess file).
Then I've got a new problem,
With direct link, The OMA.DRM.Message is correctly saved with forward lock, both on 3650 and 6600.
With OMA Download, the Download Descriptor appears correctly, but when I accept the download, a "Connection expire" message appears to download a 19kb drm message or a "Download Failed" on a 2kb drm message download.
I've checked my url, everything seems to be ok....
(on both 6600 and 3650, my real message is "Expiration Connexion" in french).
I've tried it on 3 different Download Descriptor...