Try this:
Shape conductorCable12shape = panelSheet.Drop(conductorCable12, String.Format("Key = {0}, Value = {1}", drop.Key, drop.Value));
String.Format
formats the string; it replaces the
{0}
with the key and
{1}
with the value.
EDIT: you said in your comment that it takes 3 arguments. Try this:
Shape conductorCable12shape = panelSheet.Drop(conductorCable12, drop.Key, drop.Value);