RTP ruined my fat!

Possibly soon-to-be-BeOS refugee downloaded and installed QNXRTP as a
file in my C: partition on a multi-partition system.
It would not boot.
Boot messages:
/.diskroot file for root not found on any filesystem
starting with safe mode
Unable to locate devc-con.

Shame. QNX looks like an interesting and funky alternative…

BUT: now I cannot boot Windows or BeOS. The bootmanager (BeOS Bootman)
runs but my main BeOS Pro partition won’t load (error message is
something like “cannot mount /dev/disk/ata/atapi/hda-9”)
Windows defaults to a diagnostic screen then hangs.
It will boot my Debian partition OK.
Using a boot floppy I can snuffle around in DOS. I get some read errors
from C: but my other FAT partitions D: E: and F: are fine. I can even
launch a BeOS Personal Edition on the E drive. But from within BeOS PE I
cannot mount either C: (error message is “General OS error”) or my BeOS
partition (“bad file descriptor”).

Any ideas?
Is this known behaviour by QNXRTP?

I suppose I must reformat C but In particular I don’t want to lose my
BeOS data. I’m guessing RTP has overwritten “something” at the start of
the BFS partition; possibly it doesn’t recognise BFS as a valid
filesystem and called it something else??

One thing I can do is launch a Diskprobe program in BeOS PE that can
read and write raw data on every partition. I’m willing to try to
rewrite the “file descriptor”, whatever that is, if someone can tell me
what to look for.

Sorry for the long post.
Nigel Malthus.