Link: Blog O' Rama: SugarDaddy: XSQL Troubles.
I also received this error sporadically while working the exercises, but as I kept trying, it eventually worked. I have a feeling we were having problems because we were all connected to the database simultanously during class, which exceeded the number of possible connections.
I believe this observation to be correct, and we will do something at the beginning of class on Thursday to fix it.