Good news! We have released a patch for OpenTok. This patch is meant to deal with the black screen issue. Our internal testings show that it is more stable (less crashes) and that there has been no black cam issues. Also, this improvement seems to show in all three supported browsers (chrome, IE, firefox). However, this was just internal testing. If you guys still experience this, do the following:
1) Clear both flash cache and browser cache.
3) If it still doesn't work: for crashes, report here; for black screens, report here.