Dennis,
I don't know if this is any help (as I don't own the 9000),  but on the PSR2000,  you can delete ALL User Flash Memory 'all at once' by going to the Function> Utility Page and then under Factory Reset, select the 'Files and Folders' check box. WARNNG: Make sure you really want to delete everything before preceding because once it's gone it can't be recovered. I strongly suggest backing all USER flash memory to  floppy (and then to CD) FIRST just in case you later find you really needed them. 
Hope this helps,
Scott
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