Win95 and psql - unsupported frontend protocol

I'm new to PostgreSQL, forgive my ignorance.

I'm using psql on Win95 over TCP/IP to access PostgreSQL on my Linux
box. When I do:

psql -h tower -d john

I get:

Connection to database 'john' failed.
Unsupported frontend protocol.

Anyone know what this means, or where I can find info on it ? I've
grepped everything I can find, but to no avail.

Thanks,
  J J