newish nobby nic Evo tyres
could be your problem, I have been running tubeless with various tyres and rims for 18 months now,
lots of problems, but also months and months of uninterrupted riding,
at MM 2010 bought a pair of Nevegal UST, put these on my XT UST wheels mid race and they went on a dream with a track pump, no washing up liquid and shaking the wheel to seal, straight on and inflated first time, used them for 4 months solid after that,
decided to use the front tyre again for this winter, on the same wheels, it just will not lock into the rim, tried inflating with an air compressor and no luck, now having to use the tyre with a tube