I believe he is referring to Flock, hence "I deinstalled and reinstalled Flock: no luck".
Either way though, whats the exact error message you receive? Is it something to do with mozcrt19 missing? Have you tried Flock in a new sandbox to see if it works correctly?
Anyways, as Guest10 pointed out, Flock is discontinued and has been for about half a year, so I really advise you don't stick with it anymore. Flock was always behind in terms of browser security as well as being versions behind the official Firefox (or towards the end, Chrome) versions. I can only imagine how unsecure it must be now.
If you want a more recent (and probably better) "social browser", maybe Rockmelt would be a better choice now.