Eagle Questions 7.4.0 and 6.5.0

[Faringdon]

Hi,
I just put a via into the layout...named it to a signal, then tried to connect to it from that signal, but it wont connect...just get the yellow cross...do you know why it wont connect?
I dont know where it went now but an error message complained it couldnt connect it on two of the layers (its a 4 layer board).
In fact , i cant use a via to go from bottom to top layer...it says "cant set via to layer 16". Do you know whats wrong?

I was pasting lines into the eagle.scr file (to carry through my assigns)...but i thought i had deleted all my modifications.

So do you know why Eagle wont let me use vias?