Problem w/ 8.1.6 Thin Driver and Oracle 8.0.5

Question

I am attempting to connect to two data hosts.
One is Oracle 8.1.6, the other is Oracle 8.0.5. The DB Admin insists the user name and passwords are the same for both.
I am using the v8.1.6 100% Java thin driver under both JDK v1.2 and v1.3. My OS is Windows2K Professional.
I can always connect to the 8.1.6 database but never to the 8.0.5 database under any circumstances. The error I receive when attempting to connect to the 8.0.5 database is:
java.sql.SQLException: Io exception: Connection refused(DESCRIPTION=(TMP=)(VSNNUM=134238208)(ERR=12505)(ERROR_STACK=(ERROR=(CODE=12505)(EMFI=4))))
Does any one have some insights here?
My test code fragment is as follows:
try{
Class.forName( "oracle.jdbc.driver.OracleDriver" ).newInstance();
String dbURL = "";
//dbURL = "jdbc:oracle:thin:@host1:1521:data_source_8_1_6";
dbURL = "jdbc:oracle:thin:@host2:1521:data_source_8_0_5";
Connection con = DriverManager.getConnection(dbURL, "test_user", "test_user");
java.sql.Statement stmt = con.createStatement();
String sq1String = "SELECT * FROM DUAL";
java.sql.ResultSet res = stmt.executeQuery(sq1String);
int rows = 0;
while(res.next()) {
rows++;
System.out.println("rows = " + rows);
catch(Exception e) {
System.out.println(e);
null

Answer 1

tnsping is working correctly. We can ping the host and it is listening on port 1521. Likewise, there are other applications inhouse using this datasource.
Since first posting my question, I have also tried running the test program on WinNT. Same problem arises.
Other suggestions?