I have made all of this.
I always install extension through Extension manager (E.M.) and Dw closed and when it finished, close E.M. and launch Dw and wait that WebAssist installer complete the installation.
1. Are there some preference files or similars that I can delete?
2. I forgot to tell a thing: the annual Adobe licence fee expired and now I am in a trial month waiting I renew. Can be this the cause? Because this is the only thing that levels the two machines (MacBook Pro10.9.5 and Mac Pro10.8.5).
3. If the E.M. doesn't respond (as I said on Mac Pro10.8.5; E.M. window appears but the multicolor-cursor turns round until I kill it), what can I do?