I have been using avast for years, I recommend it to most of my friends and even put it on my parents computer. I recently purchased a new laptop with Windows 8.1, deleted the default Norton crap that comes on computers and installed Avast Pro, with license, so its a paid version of the software. Was running great.... then....
After Windows 8.1 did a "features" update, I had already turned off the windows update due to this being my 3rd attempt at getting avast to run on this machine without the htmllayout.dll error. Yes, I reset the computer back to factory specs each time. This is a brand new system out of the box so I had nothing to loose.
This is not an Avast issue, this is a windows issue somewhere. I have been monitoring my computer closely after my 3rd reset to factory, and the avast was working perfect until yesterday I turned off the computer and it did a features update, when I turned it back on, I got the error, after checking the log files, the only thing that happened was 'some' features were updated but I can not see which ones.
Running malware, repair tools, scannow and just about any other fix has failed for me. Only way I have been able to fix it was a factory reset. I will be doing it again today, installing Avast Pro again, and then creating a restore point to see if there is a short cut to the fix other than a complete reset. I will update the post when I complete this task today.