Speaking from my personal experience on one XP Pro SP3 system: I did a full offline installation of avast 9 (aka "2014") [i.e., saved/backed-up my customized settings, uninstalled avast 8 via Control Panel, rebooted and ran aswClear in SafeMode, rebooted and installed avast 2014, imported my customized settings] and have had no problems whatsoever.
I was so happy with the way 2014 was running there, that about 2 weeks later, I tried the same procedure on my Win7 system, only to have it FAIL to install... despite repeated attempts. Go figure?!? So I reverted to running Avast 8 on my Win7
Infer what, if anything, you wish. The fact that it worked smoothly for me on XP doesn't guarantee the same for you. So many factors (hardware variations, and especially the particular security [MBAM PRO, third-party firewall] programs you're running) my lead to alternative results for you.