OK, So I have 2x HIK DS-2CD2135FWD-I domes. 1x Hik DS-2CD2732F-1 dome (very tempermental) and a bullet - DS-2CD2T35FWD-I5.
Not sure what the NVR is, have not had time to get in the loft and have a look (but its working fine).
What could cause login errors? You can log into a camera fine...