"Add via failed" message

I get that message when I try to add a via to an internal layer.

I had done the following before trying to add the via:

1.  Plane>Place Plane shape to place a plane shape corresponding to "GND1".

2.  Editor Control > Layer Settings to pair layers 4 and 2, where the plane shape was created on layer 2.

After that I started a "GND1" connection on layer 4, plowed and double-clicked to connect that trace to the "GND1" plane shape on layer 2 and got that message.

Ken