pre-install error: "Error mounting device: X as Y: invalid argument"

[Ben Lancaster]

Hey,

I'm trying to install FC5 on my x86 box, whilst maintaining an LV  
group from a prior FC installation.

I have:

250GB - hda
200GB - hdc

My LVM is roughly 100GB of hda and all of hdc (resulting in a 300GB  
LV). The group is already formatted using JFS (and the installer was  
launched with "linux jfs" at the first screen), and has data on it  
that I *need* to keep.

During the installation, I chose to do a clean install, using a  
custom partition structure:

hda1	100MB	/boot	ext3
hda2	117GB	/	ext3
hda3	2GB	swap

hda4-5 are part of my LV group (MediaGroup).

The partition structure is identical to the one I set up when  
installing FC4, and I had done a few clean reinstalls of FC4 whilst  
using this partition structure. hdc and hda4-5 are not set to be  
formatted.

After selecting the packages to install, and confirming all (thus  
formatting hda1-3), the installer begins, but then bails out with:

--
Error mounting device: MediaGroup/Media as /Video: invalid argument
This most likely means this partition has not been formatted.
Press OK to reboot your system.
--

Am using the latest CD ISO torrent, and my installation media has  
been tested and verified.

Can anybody point me in the right direction as to what's going wrong  
and where? It strikes me as an odd error message, since I  
specifically asked the installer not to format the lv group!

Thanks in advance,

Ben