payne,
Firstly, I use Avast Home on an ME system and it works fine, so we need to try and find out why it will not work on yours.
Secondly, what version of Avast are you installing?
Is your copy the Home or Pro version?
The latest is build 4.1.418 and the database is 439-2.
We can try 2 more things. Suspecting STILL a bad installation file, Go into the Add/Remove again and highlight Avast. Click Remove and you will be given the option to Repair Avast. Try that.
Reboot the computer and try again.
If this fails, then it is possible that your copy of Avast itself is corrupt and no matter how many times you install it, it will not work. In this case, I would download a fresh copy of Avast from a different site or mirror, and then try again. (You can use the same key)
BUT THIS TIME before installation....go to
www.avast.com, Downloads.....and find the Program utility Avclear.
Use this to remove all remnants of Avast.
Reboot the computer.
Then use the new copy and install.
Hopefully this will take care of it.