There have been login problems of one sort or another since at least last autumn, as detailed here (if this link works)
http://www.cpcontacts.com/uk/forum/s...ead.php?t=1387 which are still outstanding.

I would suspect the solution lies somewhere in the Admin settings, as I am a member and regular user of another site (and another kink ) which uses exactly the same software, and I have no problem with that site whatsoever.

The only difference I can see is that that site uses release vBulletin® Version 3.5.3 whereas this one uses vBulletin® Version 3.8.1