Glad to hear you have it solved!
Thank you for asking the question that prompted me to try and figure this out.
I've seen the same issue, and just ignored it until now when I had time to dig into it...
Yea, notepad has "memory limitations" and some other program can often open a file that notepad can't.
The sad part of this is (You, I, or any user) should not have such a difficult time finding and seeing "History Logs and Reports".
IMHO Avast should allow a user to easily see reports and logs no matter what the OS version and Avast version ...
Even sadder, you're getting help from ME - no Avast expert by any means ...
You asked the question 2 days ago ... where is the Avast "expertise" ?
I'm following this thread, as I'm about to jump ship
http://forum.avast.com/index.php?topic=149366.0 I don't know how to mark a thread as "solved" etc. in the Avast forum.
An Avast forum Admin would need to help with that.