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To the Original Poster (and anyone else)
I had a similar (but even bigger) popup advertising Google Chrome that was caused by my not paying attention during installation and missing a pre-checked box.
I suspect that somewhere sometime you checked (or didn’t un-check) a box that said you wanted to see advertisements of upgrades and special features.
You can see the thread that I started, the offending file (Offers.ini) and my solution and commentary at: http://forum.avast.com/index.php?topic=140849.msg1027907#msg1027907