After updating to the 12.6 AMD driver from the 12.4 driver, I've found that World Machine 2 no longer works on my PC. It gives me a crash related to atioglxx.dll which is AMD's OpenGL driver.
It worked fine on the 12.4 drivers, so how would I downgrade my OpenGL driver to the 12.4's?
I can obtain the atioglxx.dll from the 12.4 driver installer if thats any use.
Same has also been happening to Neverwinter Nights 1, after upgrading from the 12.2 drivers.
Your best bet would be to uninstall the current drivers, reboot if prompted, and then reinstall the older 12.4 drivers. When you start mixing and matching DLLs from different releases, you're just asking for trouble that will be nearly impossible to sort out.