There appears to be something missing at the start of the location you gave.
You don't say what your Operating System is as it has different locations depending on OS.
Look in:
C:\Documents and Settings\All Users\Application Data\Avast Software\Avast\report\aswBoot.txt file (XP location)
C:\ProgramData\Avast Software\Avast\report\aswBoot.txt (Vista, Win7 location),
The folder location in win7 (and later) may be hidden by windows folder options.