Certain Vertices will not paint with the Paint Skin Weight Tool

[meyercLQ7VZ]

I'm trying to reduce the amount of vertices a joint is bound to, but some vertices will not paint for a reason I do not know. I've tried rebinding the skin to the model but with no luck. Any ideas?

[Kahylan]

Select the vertices you don't want to be affected, opend the paint skin and use the flood option with the value set to 0

[stephenkmann]

make your brush bigger..  I think you are just missing the points