I don't see how you could have affected the switching of the lamp that
works as a 3-way by adding an inline switch in the lamp cord.

I could be wrong. It happens regularly.

Are you sure you are using a 3 way lamps?

Hi Terry:
We initially rewired them with 3 way sockets, and
worked perfectly. On adding the inline switch(which turns them on and off
fine), we lose any adjustability on the socket switch. If we turn the socket
switch, we get on and off only. No progression.

Thanks