It is not a problem with the CD or drive. The UBCD program launch doesn't work on this specific machine and, coincidently, ES-Tools also has a problem on this machine. It is all fine if I boot any of the two CDs on another machine. I haven't checked all machines, so I can't say if there is any second machine displaying the same problem.
In theory, according to the info you provided, you can't be 100% sure the CD drive isn't the problem. You may try verifying the CD media against the downloaded/customized iso image, using the same computer. Several (not all) burning tools have the "verify" function. I am not talking about the setting to "verify" right after the CD was burned, but a separate "verify" function. There are also specific freeware tools that doesn't burn a CD, but only check / compare the burned CD against an iso image.
I'm not 100% sure, but convinced to a certain extent that the BIOS update must have made the difference.
AFAICS, none of the BIOS settings were changed by the upgrade and the OS (2008 R2 x86-64) is working just fine.
Note: I apologize in advance if you already know the next info, but some other (newbie) user might want to know what to do.
Usually, current OS's adapt to the new BIOS. But DOS is not such an OS (meaning, something like "PlugAndPlay").
In any case, it is recommended to "clean" the BIOS data after a BIOS update, and then set it again to what it is suppose to be.
I have experience with Gigabyte mobos + AwardBIOS. I have seen situations where it "seems" that everything is fine after a BIOS update, but after a while I find that "something is not exactly working as it should". Clearing the BIOS data solved the problem.
There are command line parameters when running the DOS-based flash utility to "clean" all the BIOS data. But, if you can power off your system, take out the cmos battery from the mobo for a couple of minutes (NOT seconds), replace it again, boot into the BIOS, set "safe" defaults, save and boot again into the BIOS and set the values to what it should be, and "save and exit" the BIOS, then it should be enough to clear all BIOS settings.
Before taking out the cmos battery, you can write down the BIOS settings if you are not sure what they should be.
Fix: Some of 1000 GB (1TB) HDDs will be detected size error
Update CPU ID
Disable PCI prefetch
Using 1TiB size HDD is one of the reasons for HDD manufacturers to update their software tools. So I would suggest, as a general rule, to try using the latest versions, which were updated in their respective websites since UBCD503 was released. You can customize UBCD with those tools.
You can also try different boot options (more "defensive" DOS boot modes, disabling certain drivers during the DOS boot process and so on).
it appears that I will never be able to use UBCD on it in case I *need* it
Since HDD manufacturers' utilities are DOS-based tools, may I suggest changing the advanced BIOS settings? You can try disabling Virtualization, x64 settings, special OC settings, and so on. I mean to try this step only after trying the first one I suggested, "cleaning/clearing" the BIOS data/values as I suggested before.