@Laserfan ... thanks for the reply. I was actually thinking along similar lines before I noticed your post. I had noticed that my page file settings were not optimal and I wondered whether that was having anything to do with the problem I was having. Anyway, I'll get to that in a minute, but for now, and in short, I have a major update ...
I'm back working again!
The bad news is I've no idea what the issue was, but I'll outline my attempts to fix just in case someone else is having similar issues and they find this post of some interest.
As originally suggested, I tried my TTH02 media at 8x, cleaned the drive, and upgraded to the latest writer firmware to no avail. All DVD-Rs and my test DVD+RW failed at 66%. I had made a fair few coasters at this point and decided to not waste anymore DVD-Rs and just continue using the +RW whenever I wanted a test burn. I then started to look at my setup.
In brief, I had two new 500GB SATA drives, but I also had connected up my previous system disc in order to transfer files. Windows had set my page file at only 2GB despite my having 4GB of RAM. I also had manually switched a lot of drive letters during setup, so I looked into the 'MountedDevices' key as suggested by Laserfan, but all seemed ok. I proceeded to mess around with the page file settings, setting page file size to approx 6GB, and across various drives, doing a test burn on the +RW each time. I noted a couple of times that while it still failed, it didn't always fail at 66% anymore. I saw this as some degree of progress and tested significantly before exhausting my options and settling on a small page file on my system disk and the majority of the 6GB page file on my data disk.
I then opened up the PC again looking for loose connections. I noted that I had forgotten to connect the Front Panel Audio Connectors (R-Out, L-Out, GND etc) and did a test burn thinking unconnected cables had to be the issue, but no joy. I tried burns on different IDE connectors and IDE cables, with drives disconnected, again with no positive results (the 66% figure was now back).
I was all but resigned to replacing my drive, as suggested by LIGHTNING UK!, when for some reason I ended up trying a different +RW. Bingo! Success. I tried a different image, same result. I connected everything back up the way it should be .... same result! I retried my original test +RW ... failed at 66%. I tried one of my -Rs ... success! In short, I had somehow fixed the problem since my last DVD-R test after the firmware update, but because i was using a dodgy +RW whenever I tested a burn, I never noticed it.
Therefore, I reckon it's one of the following, although I can't be sure which. Any ideas as to the likely culprit?
1. Optimising the Page File. (if i had to pick one, I'd go for this)
2. Connecting up the Front Panel Audio Connectors (wouldnt have thought these would affect burning, but I don't know).
3. Re-seating/connecting all cables and components inside the PC.
I'm delighted I have Imgburn working again, as it's perfect for my needs. Thanks to both LIGHTNING UK!, and laserfan for their responses, and attempts to assist me.
Phil