I have a very easy solution to this. It is a slight modification to the post above mine. This fix did not require a reinstall of Avast!
Step 1: Browse to the c:\Program Files\Avast Software\Avast\Setup
Step 2: Copy the HTMLayout.dll
Step 3: Browse to the c:\Windows\System
Step 4: Paste the HTMLayout.dll into this directory.
Now launch Avast! Internet Security.
This took me to a splash screen that says "Complete your upgrade to Avast! 2014
It had only a Continue button, I clicked it, and now the Avast GUI come up just fine.
Try these steps and let me know if they work. This fix did not require a reinstall of Avast!