First the good news:
Yesterday I received an email notification from Google that my AdSense account had been reinstated. It confirmed that the original reason for the ban was the inclusion of the Be Nice feature in earlier versions of AdSense Manager (this has now been removed).
This also means that I can continue to develop AdSense Manager as intended - get your feature requests in now!
Now the bad news:
It appears that some people are still using older versions of AdSense Manager on their blogs. If you are not yet using v2.4 UPGRADE NOW!
Thanks for all your support.