Question: Skype has been disappeared from GNOME top panel. So after closing it, it stays running, but invisible. Reopening it from application menu gives crash, because it is running.
Answer: It has very simple solution. Look at top panel, there must be a little gray icon of Notification area. If it exists, remove it from panel, thenr restore it with right click->add to panel->Notification area. If it doesn’t exist, then do same thing, add it to panel. Then quit from Skype, and then reopen. Everything must be ok.