El Capitan - Login problems with SIP enabled
VirtualBox is not compatible with El Capitan. From the VirtualBox build instructions page:


  Prerequisites on Mac OS X: 10.6.x (Snow Leopard), 10.7.x (Lion),
  10.8.x (Mt. Lion), 10.9.x (Mavericks) or 10.10.x (Yosemite) running on Intel hardware.