I'm not a qualified gas or boiler installer so plse take this as a starter for ten.
Baxi and other web sites would suggest that for the E133 error you should check that the condensate drain pipe isn't freezing up. If this isn't it, then the next likely culprit seems to be the igniter electrodes (apparently an known problem ... ) There are other possible causes as well.
However, mine only shows the E133 error so have no ideas about E168.
Hope you get more help from others who are better qualified than me.
Biggles
December 2010