Another information.
My DRM2.key is:

<DRM2WMV2>
<KID>6f98cef7effbe280</KID>
<SID>AAAAAAAAAAAAAAAAAAAAAAAAAAA=</SID>
<INFO></INFO>
</DRM2WMV2>

but the third line is:
<SID>AAAAAAAAAAAAAAAAAAAAAAAAAAA=</SID>

Is it correct?