That is an odd OS/boot loader combination. P530 V6.0 should have BL 3.4 with it.
https://www.hpcfactor.com/support/cesd/200199/mobilepro_900900c_firm...
I would suggest firstly that you just try a different CF Card. Secondly, if that fails that you make a MS-DOS / Windows 95 boot USD for your machine and try formatting the CF Card from there. Do a full format, not a quick format and don't use a third party utility. It might be doing clever things to the file system like adding VFAT support or backup FAT.
If C+F doesn't work after that, then try the serial method
(this assumes that you have the MP serial cable of course
)
1. copy the SABOOT.NB0 to the CF card and put in the MP900
2. Run a terminal program e.g. Putty or HyperTerminal
4. Use 115Kbps and software xon/xoff flow control. no parity, 8 bits and stop bits 1.
5. Connect the serial cable to the H/PC
6. You should see the bootloader saying hello in the terminal window
7. Bull the AC and batteries to hard reset your 900/900c and press ESC when prompted
8. At the boot menu type 1 to update the bootloader