@Ashutosh Kumar try also to netlist in xschem with the LVS option mentioned above enabled (and with .subckt / .ends lines in buffer.spice) I don't know if the top level must be inside a .subckt or not, however they should match, either both in a .subckt or not.

@Ashutosh Kumar: Both xschem and magic are able to generate netlists with and without a

.subckt

...

.ends

wrapper. However, it is always preferable to declare all pins and include the subcircuit wrapper in both netlists, if possible.