This is just a +1 to say that this problem persists. Here's my experience:
Avast! prompted me to upgrade from 8.0.1497 to 2014.9.0.2006. The upgrade seemed to run normally, but I noticed an error from a CMD window when the system was shutting down. After that I could not boot normally -- boots took 10 minutes and no programs would launch. I couldn't get Avast! to run at all -- it showed an RPC error each time. I was unable to repair or uninstall it. I rolled back to the restore point that the upgrade had set and was able to boot normally. Avast! still wouldn't run or uninstall, but I was able to launch a browser and download the avastclear program.
The rest of the process ran as expected (boot to safe mode, run avastclear, reinstall Avast!). Unfortunately, since Avast! wouldn't run I couldn't back up my settings first.
That's two hours I'll never get back.
This happened on a Windows 7 Professional 64-bit laptop, SP 1.