The version you are trying to remove is an older version, you may want to download the latest version and try that if there was a problem with your current version.
If you are determinet to get rid of the avast installation a visit to RejZors site at http://www.security-ops.tk/ and download the avast! External Control, a small executable tool to access certain functions within avast. There is a brutal Uninstall tool in there that should do the trick.
Since you have made attempts to uninstall already this may not work I don’t know, as Artras, said you may need to reinstall first.