System: ACER Aspire 4935 with Windows Vista and Acer Bio protection.
Former antivirus software: avast! Home Edition v4.8.
Several months ago I bought a license for avast! 4 Professional Edition, 2 years.
After updating yesterday from avast! Home to avast! Pro v5 (which seemed to function without serious problems) on my next logon a warning did appear: “Logon process initialization failure: Interactive Logon Process Initialization has failed. Please consult the event log for more details.”
Well, I didn’t even get as far as that … again and again and again!
Only after entering safe mode and deinstallating avast! Pro v5 the system did appear to function as before.
Now avast! Home Edition v4.8 is installed and seems to be stable, but what about paying for a professional version which does not work?
Hoping for help with this problem and grateful in advance!
read my post i got same error 
Hi ejust,
Welcome to the forum, this problem seems has been solved, please refer to: http://forum.avast.com/index.php?topic=53782.0
Or I wrote it personally here: http://catatan.legawa.com/2010/03/fixed-crash-windows-login-with-avast-5-on-acer-machine/
Regards,
Cahya.