scream machines glitch

ok something is wrong with my scream machines. Im trying to make supports on a ride and they usually let me move the free any where but now it wont let me go to a certain point for exaple... if i wanted to put a node at 38.4' it would put it at 35' or 40' nd i restarted my computer and i dont know what to do[V] HELP PLEASEE

[Dirk_Ermen]

snap is on, you can enable\disable it with the 's' button