CD Closed despite CLOSE_SESION Flag

Hi all… I’ve got another problem that I hope someone can help me with…
I am burning a CD with the NERO_BURN_FLAG_CLOSE_SESSION flag to allow for further burns in the future. The first time the CD remains open and I managed to burn more files a second time. However, after this second session, the CD seemes closed despite the flag. (When I look at CDInfo, it gives me a figure under UnusedBlocks instead of FreeBlocks). The strange thing is, I managed to write to the CD (a different one) a lot of times earlier before I included the code to EstimateTrackSize.

Am I doing something wrong?

    nfstoSize.MediaType = NERO_MEDIA_CD
    nfstoSize.BurnFlags = NERO_BURN_FLAG_SIMULATE + NERO_BURN_FLAG_WRITE + NERO_BURN_FLAG_CLOSE_SESSION
    nfsdcData.BurnOptions = NERO_BURN_OPTION_CREATE_ISO_FS Or NERO_BURN_OPTION_USE_JOLIET
    nfstoSize.FileSystemDescContainer = nfsdcData
    
    ' estimate track size
    DriveReady = False
    Drive.EstimateTrackSize isotrack, NETS_DATA Or NETS_FILESYSTEM_OVERHEAD Or NETS_EXACT_SIZE, nfstoSize
    ' wait for event done and handled..
    While Not DriveReady
        If BurnCancelled Then Exit Function
        DoEvents
    Wend
    
    ' burn it!
    isotrack.BurnOptions = NERO_BURN_OPTION_CREATE_ISO_FS Or NERO_BURN_OPTION_USE_JOLIET
    Drive.BurnIsoAudioCD "", "", 0, isotrack, Nothing, Nothing, NERO_BURN_FLAG_SIMULATE + NERO_BURN_FLAG_WRITE + NERO_BURN_FLAG_CLOSE_SESSION, "0", NERO_MEDIA_CD

Additional info… under the OnWaitCD event I’m getting the WaitCD result as:

NERO_WAITCD_WRITEPROTECTED
i.e.
“This disc is not writable.
Please insert a writable disc…”

Does this WriteProtected means the CD is finalised or something else?