If you get the error “Another program has already opened a LocalConnection with id ‘_flexcover’. No coverage data will be recorded.”, do the following:

1. Open Task Manager and kill any instances of CoverageViewer.exe (or your Mac equivalent).
2. Close all browsers.
3. Close FlexBuilder.
4. Close Yahoo! Messenger (or other client that hosts the Flash Player).

#3 did it for me.

I was using FlexCover 0.81.