may be something wrong with newest versions (0.4.1e and 0.4.2) ?
my 0.4.0 VPS with well-known (bootstrap) IP can work ~2 hour before "java.lang.NullPointerException", whereas my anorher VPS 0.4.2 with unknown (for public) IP hardly survive 30 min.
Nothing special AFAIK, maybe BCNext added something, I don't review all the changes...