I ordered a 2GB CF card and that finally worked. There is either something wrong with the 8GB CF card that I received from AMIGAstore.eu, or my version of A500/KS/WB/WDToolBox can't handle drives that big. But all is well now.
I do have another Amiga, a stock CDTV with an AmiTrix SCSI-TV + SCSI2SD - and I really didn't want to mod it, so I'm glad the new CF card worked.
Thanks.