netmeg - 12:36 pm on Sep 8, 2012 (gmt 0)
Well none of us can speculate because we don't know the sites (and I have much higher CTR than that on some sites, and much lower on others)
When I've seen sites that got notices of invalid activity, it's usually been a case of clicking on one's own ads (which I'm sure Donna knows not to do) or some kind of unusual traffic pattern (like from a country that doesn't usually visit the site, or from a small range of IPs, or something similar)
It does seem a little unusual for them to call out both sites, but you say they're under two different accounts. Could the multiple accounts be what the problem is?