This was a new site in CS5 but no server defined
Thanks Ray. This was a new site in CS5 that was minimally defined per the new feature set in CS5 of only having to define a name and local root. I went back and added a remote server which allowed the extension to open. But the extension runs very slowly, hangs up when adding new pages, moving pages in the tree, etc. while still only defining them. I have seen this in general with WebAssist extensions which provide page previews in the wizard but this one is basically dramatically more unstable than others. Machine is a 2xquad core Xenon with 16GB RAM, running XPP SP3, with no antivirus/firewall/etc., strictly setup for dev work. Will keep my eyes out for the next release as I'm sure these issues will get sorted. Cheers.