7.0BETA2: Can't use with Parallels virtual CD-ROM drive

Dear all,

I downloaded and attempted to install the 7.0-BETA2 ISO on a Parallels VM 
yesterday, and fairly rapidly ran into problems.  I configured the ISO to 
appear as a CD-ROM drive in the VM, and booted: it happily got to sysinstall, 
but when I began the install, sysinstall was unable to mount the install CD. 
Booting to an existing 7-CURRENT VM, I found that it also was unable to mount 
the CD, but that I could install from a 6.3-BETA1 ISO without a problem. 
Testing from the command line, "mount -t cd9660" on 7.0 returns:

mount: /dev/ac0 : Input/output error

The same command on 6.3 successfully mounts the image.  On the general theory 
of things, I tested mounting the 6 ISO on 7 (failed) and the 7 ISO on 6 
(succeeded).  In both 6 and 7, the virtual CD-ROM drive appears to probe fine:

acd0: DVDROM <PRL CD-ROM [1]/FWR10003> at ata0-slave PIO4

In both cases, the drive continues to show up fine in atacontrol:

     Slave:  acd0 <PRL CD-ROM [1]/FWR10003> ATA/ATAPI revision 4

I tried reconfiguring Parallels to move the ISO to the second virtual ATA 
controller and that didn't make a difference either.  I was wondering if 
anyone else had seen this?  It sounds like it may be a change in the ATA 
driver?

Robert N M Watson
Computer Laboratory
University of Cambridge