When Dave Lister and Kryten were judged by The Inquisitor, they suffered the fate of the unworthy. They were surgically removed from time and replaced by alternate versions of themselves, "the sperms that never made it". This version of Kryten took his place as a service mechanoid and lived a similar life to the original.
He was similar but not identical to the original Kryten, with an identical body and similar voice but a distinctly different facial structure, perhaps caused by being modelled by a randomisation program.
When the original Lister and Kryten escaped The Inquisitor, they triggered a security alert because their palmprints could not be recognised by the doors. The crew of Red Dwarf arrived, including the new versions of Lister and Kryten. They were people who had never been given the chance of life before The Inquisitor intervened.
As they took the intruders to the brig, the crew was attacked by The Inquisitor, who was trying to complete his work by destroying the originals. He instead managed to make the new versions of Lister and Kryten die in an explosion.
The alternate timeline was reset to normal later, when Lister tricked The Inquisitor into erasing his own existence. This meant that the alternate Kryten had never existed. (RD: The Inquisitor)