com.apple.launchd DumpPanic - System hangs for 5 mins on boot

We've been having a problem with one of our Mac Pro's for a while now.

It hangs for about 5 mins on boot - slowly gets past grey screen and hangs on blue screen.

The Mac is a 2.66 Quad-Core Intel.

The problems began a while back, when running photoshop - the scratch disk filled the hard disk entirely on a really large document and the whole system died. On reboot the system started to hang in the boot process and has done ever since.

The system also appears to be sluggish and doesn't respond as well as an identical machine next to it.

I checked the boot log and noticed a few issues, some of which i've now fixed - ie a faulty USB device causing some problems.

This is what i've got now:

28/04/2011 12:41:53 com.apple.launchctl.System[2] launchctl: Please convert the following to launchd: /etc/mach_init.d/dashboardadvisoryd.plist

28/04/2011 12:41:53 com.apple.launchd[1] (com.apple.usbmuxd) Unknown key for boolean: EnableTransactions

28/04/2011 12:41:53 com.apple.launchd[1] (org.cups.cupsd) Unknown key: SHAuthorizationRight

28/04/2011 12:41:53 com.apple.launchd[1] (org.x.privileged_startx) Unknown key for boolean: EnableTransactions

28/04/2011 12:41:58 com.apple.launchd[1] (com.apple.DumpPanic[29]) Exited with exit code: 1

28/04/2011 12:47:10 com.apple.launchd[1] (com.apple.UserEventAgent-LoginWindow[76]) Exited: Terminated

28/04/2011 12:47:10 com.apple.launchd[81] (org.x.startx) Unknown key for boolean: EnableTransactions

28/04/2011 12:47:12 com.apple.launchd[81] (com.apple.CSConfigDotMacCert-@me.com-SharedServices[85]) Exited with exit code: 1

What i've tried:

Repair Disk Permissions - using disk utility and disk warrior.

Cleaned cache and settings using Maintenance and Onyx.

Turned off automatic time/date setting from server.

I then backed up and reinstalled the OS.

The OS is now on a separate 160GB SATA drive, with the previous 500GB SATA system drive as data storage.

I have installed back to 10.5.8 and still get this problem.

It seems to me that there is a delay of about 5 minutes after this line:

com.apple.launchd[1] (com.apple.DumpPanic[29]) Exited with exit code: 1

However after LOTS of googling and scouring forums i can't seem to find a definitive answer as to why this problem exists.

Can anyone help me?

My next step is to book an appointment with a Genius, but thought i'd ask on here first.

Another strange conundrum is that if i try to upgrade to Snow Leopard, i insert the disc - open up the installer - click restart and the system restarts, but nothing gets installed.

Thanks in advance for any support you can provide.

Cheers,

Rob