After upgrading to the most recent firmware, the camera (DS-2CD2387G2-LU) stop answering all ISAPI calls. I checked and double checked that the web authentication was set to digest/basic, and it was. After downgrading to 5.7.11 build 221009 the ISAPI functions came back on. So either there is major bug in the most recent firmware or there is some new function hidden in one of the menus, which most be enabled for the ISAPI to work.