Mac Pro 'forgets' that it has optical drives

Question

I have a Mac Pro which is exhibiting an unusual (and rather annoying problem).  It keeps forgetting that it has optical drives.  When I first turn it on, all works correctly.  I can access both optical drives normally.  After a while, however, it seems to 'forget' that it has optical drives connected.  It hasn't, so far, forgotten that it has optical drives while they are in use.  I can watch a DVD right through, for example, or write a disc - but if I leave it for too long without accessing the optical drives then it will forget that it has any until I next restart it.  If there is a disc in the drive when it forgets then I can't get the disc out until I restart, and if I try to access the drive then the program that I try to access it with will crash - and need to be force quit.  If the program is Finder then Finder won't restart until the computer is restarted.
The problem is limited the optical drives - I haven't, so far, had any problem with the hard discs.  If I don't use the optical drives at all then I can leave my Mac turned on indefinitely without difficulty - with the proviso that it will need restarting if I need to use the optical drives.
Troubleshooting done so far:
Swapped the drives around and tried running with one optical drive only (no improvement seen)
Checked the system logs for clues and discovered them to be worryingly full of 'crap':
18/03/2012 16:20:27.000 kernel: IOSurface: buffer allocation size is zero
18/03/2012 16:20:34.000 kernel: miBnot otootBooCa tecnate cache hon bad hcrme oinn hitrate
18/03/2012 16:20:34.000 kernel: btCatneaa oech: ctcace:oted hrmB ootiCache: terhineco uld nototrnmin  tubaaermiatnate  ctaoulte e
18/03/2012 16:20:34.000 kernel: d hlddcache on bad hitrati te
18/03/2012 16:20:34.000 kernel: e nracte
18/03/2012 16:20:34.000 kernel: notot t cateacrmeriBcoomihnaBoBootCache: could not terminattee  ccanate cache on bad hitrate
18/03/2012 16:20:34.000 kernel: ahcheeo och ntCatCchaec: baon BootCache: could not terminate cache on bad hitrate
18/03/2012 16:20:34.000 kernel: bae  d heh: cioutde  onB oclbraodu lnaoodd hh ntootitCt trn bachee tadrm: i coaulhitee
18/03/2012 16:20:34.000 kernel: rtinamitd rnanot teramitte
18/03/2012 16:20:34.000 kernel: te ctrachenae
18/03/2012 16:20:34.000 kernel: te e cacach aBootete
18/03/2012 16:20:34.000 kernel: che on CB obaad hitnron ootCate
18/03/2012 16:20:34.000 kernel: achchBoee ba:: ot coBoCad hbaiBootCache: could cchonotue td:l  hd ittrarerminateulonc cache on bad hitrate
18/03/2012 16:20:34.000 kernel: oattte
Specification:
Mac Pro (Early 2009)
Processor 2.66 Quad Core Xeon
Memory 12GB 1066 MHz DDR3 ECC
Graphics Nvidia GeForce GT120 512MB
OS Mac OS X Lion 10.7.3
Storage 2*2TB Seagate, 1*500GB, 1 Pioneer BDR206D, 1 Superdrive.
All suggestions gratefully received!

Answer 1

First, get a utility like Lion Cache Cleaner 6.0.9 and clear out all user, system, and font caches. Then try reinstalling OS X:
Reinstalling Lion Without Erasing the Drive
Boot to the Recovery HD: Restart the computer and after the chime press and hold down the COMMAND and R keys until the menu screen appears. Alternatively, restart the computer and after the chime press and hold down the OPTION key until the boot manager screen appears. Select the Recovery HD and click on the downward pointing arrow button.
Repair the Hard Drive and Permissions: Upon startup select Disk Utility from the main menu. Repair the Hard Drive and Permissions as follows.
When the recovery menu appears select Disk Utility. After DU loads select your hard drive entry (mfgr.'s ID and drive size) from the the left side list.  In the DU status area you will see an entry for the S.M.A.R.T. status of the hard drive.  If it does not say "Verified" then the hard drive is failing or failed. (SMART status is not reported on external Firewire or USB drives.) If the drive is "Verified" then select your OS X volume from the list on the left (sub-entry below the drive entry,) click on the First Aid tab, then click on the Repair Disk button. If DU reports any errors that have been fixed, then re-run Repair Disk until no errors are reported. If no errors are reported click on the Repair Permissions button. Wait until the operation completes, then quit DU and return to the main menu.
Reinstall Lion: Select Reinstall Lion and click on the Continue button.
Note: You can also re-download the Lion installer by opening the App Store application. Hold down the OPTION key and click on the Purchases icon in the toolbar. You should now see an active Install button to the right of your Lion purchase entry. There are situations in which this will not work. For example, if you are already booted into the Lion you originally purchased with your Apple ID or if an instance of the Lion installer is located anywhere on your computer.