Eagle wont let me put vias down while routing a 4 layer board

[ocset]

i have a 4 layer pcb that i am routing up.
It has layers (1*2)+(15*16).
When i route on the top and then select the bottom lyaer (16), it gives error "cant set via at -40,30 to layer 16".
It wont let me put vias down.
Do you know why?

[Jeroen3]

Your layer setup does not allow vias from top to bottom.
You need (1+2*3+16) for that.

Your setup (1*2)+(15*16):


Correct setup (1+2*3+16) without blind vias.


Check eurocircuit drc rules. (attached)

[ocset]

Thankyou, you are the Best!