i dont know where is the active file or the serial etc etc..
Send an email to sales (at) avast (dot) com with the same email you've used to bought avast and explain.
Please, upload (attach) the avast log: C:\Program Files\Alwil Software\Avast5\Setup\setup.log
(or the shorter C:\Users\All Users\Alwil Software\Avast5\log\Setup.log).
If the file is too big for the forum, post the
last 400-500 lines of it.