reference points at cross junction some times flexible but sometimes not flexible

[heichan88]

Hello,

I have some reference points at cross, on left side, they can flex, but on right side, they cannot ("failed to constain"), and I cannot trace back what is the difference of the property of the points on either sides. 

Please advice what is the difference and any rules to make it

 

 Solution: I set the work plane of the point to be reference line (v), then OK