got an alert from Google Safe Browsing

I have 2 or three sites that generate an alert from Google Safe Browsing when browse them with Google Chrome. This alert is of the type that says this website is suspicious, and do you really want to proceed.

I've checked these sites with various online malware scanners, and they always come up clean, except they report that the sites are on Googles safe browsing blacklist. So, while I can't figure out what's causing the blacklisting, since all the services look at each other's blacklists I feel that the impact of my blacklisting is reaching farther and farther. Sometimes I get these warnings in Firefox and now I am getting scary security warnings when I try to access from within my corporate network.

What can I do? Specifically, Google says to communicate with them via Google webmaster for any questions of this nature. However these sites have high PR and are part of my aspiring wanna-be tiny private network that I want to keep discreet, which is why I haven't before signed them up with Google webmaster. Since i can't figure out what's causing (or previously caused) the problem, whom do I need to get in touch with, and how, to start getting this fixed?