Hard to say about the memory, running it at a speed higher than what it is rated at (?) can cause problems in generic memory chips (or is it a brand name), without increasing the input voltage, but I'm no hardware specialist. Most memory is compatible in any motherboard provided it is the correct type (DDR2, etc.), some MB manufactures only test the larger name brands; so that would be the only ones they would guarantee, but that alone shouldn't be a problem.
So it is possible this could have an impact, though I don't know if that might be the case in the update problem, which is showing the faulting module as ntdll.dll and that avast.setup was using it at the time of the problem.
There has been a recent program update (5.0.677) yesterday, so it might be worth while downloading that and doing a clean reinstall.
- Download the latest version of avast, 5.0.677 http://files.avast.com/iavs5x/setup_ais.exe
and save it to your HDD, somewhere you can find it again (if you didn't save your last download). Use that when you reinstall.
- Download the avast! Uninstall Utility, aswClear5.exe find it here
and save it to your HDD (it has uninstall tools for both 4.8 and 5.0).
- 1. Now uninstall (using add remove programs, if you can't do that start from the next step), reboot.
- 2. run the avast! Uninstall Utility from safe mode, first for 4.8 if previously installed and then for 5.0, once complete reboot into normal mode.
- 3. install the latest version, reboot.