help please

session setup failed
all setings are correct but while running the program from command line it
gives the error.......

program:
import java.sql.*;

class aa
{

public static void main (String[] args) throws Exception
{

Class.forName("org.postgresql.Driver");
System.out.println("Drivers found and registered");

Connection con =
DriverManager.getConnection("jdbc:postgresql:post","postgres","abhi");
System.out.println("connected db");

Statement stmt = con.createStatement();

System.out.print("done!!!!");

}
Error:

G:\>java aa
Drivers found and registered
Exception in thread "main" org.postgresql.util.PSQLException: Protocol
error. Session setup failed.
at
org.postgresql.core.v3.ConnectionFactoryImpl.doAuthentication(ConnectionFactoryImpl.java:381)
at
org.postgresql.core.v3.ConnectionFactoryImpl.openConnectionImpl(ConnectionFactoryImpl.java:94)
at
org.postgresql.core.ConnectionFactory.openConnection(ConnectionFactory.java:66)
at
org.postgresql.jdbc2.AbstractJdbc2Connection.<init>(AbstractJdbc2Connection.java:125)
at
org.postgresql.jdbc3.AbstractJdbc3Connection.<init>(AbstractJdbc3Connection.java:30)
at
org.postgresql.jdbc3.Jdbc3Connection.<init>(Jdbc3Connection.java:24)
at org.postgresql.Driver.makeConnection(Driver.java:382)
at org.postgresql.Driver.connect(Driver.java:260)
at java.sql.DriverManager.getConnection(Unknown Source)
at java.sql.DriverManager.getConnection(Unknown Source)
at aa.main(aa.java:12)

G:\>