Hi Stevie,
though it is not advised as it should, LV 6 should not be considered an update of LV 5.1.
LV 5.1 should be uninstalled before installing LV6.
I also experienced problems when I installed LV 6 'over' LV 5.1.1.
Most of them were solved uninstalling completely both of them and re-installing LV6.
Hope it helps.
Regards,
Alberto