FreeMe2 works only on some WMA files

Hello,

I just tried to un-DRM (by means of FreeMe2) 6 WMA files (from 1 CD) that I bought legally. I first extracted my licence keys using drmdbg (apparently all 6 files were processed), copied the resulting drm2.key file to the FreeMe2 directory, and then used the drag and drop method to try to un-DRM the 6 WMA files that I bought. Result: 2 files were succesfully freed, for the other 4 files FreeMe2 asked me for a SID (which I did not knew)...
Can anyone help ? I have WMP version 11 final, and my IBX is 11.0.6000.7000.

Thanks in advance,

jvdv.