Java Security

hi,

i'm trying to connect to a website via https and receive an error 403

java.io.IOException: Server returned HTTP response code: 403 for URL: https://...
at sun.net.www.protocol.http.HttpURLConnection.getInputStream
(HttpURLConnection.java:709)

when using the same command in internet explorer or in a vb program, it works

the header fields show that the http error is not thrown by the receiving web site, but by the proxy (my proxy is using isa software, not netscape, so i don't know which proxy this is)
java headers (which throws the exception):
Header 1: Proxy-agent: Netscape-Proxy/3.53
Header 2: Date: Fri, 13 Dec 2002 08:51:09 GMT
Header 3: Content-type: text/html
Header 4: Content-length: 234

vb headers (which works):
HTTP/1.1 200 OK
Server: Netscape-Enterprise/6.0
Date: Fri, 13 Dec 2002 09:19:12 GMT
Set-cookie: JSESSIONID=...
Content-type: text/html
Connection: close

i am using the same proxy host, same firewall, same user in both languages, and i am using j2sdk 1.4.1.01 under windows 2000

do you have any ideas what i can do to avoid that error?
i have just started with java, and received the java sample sources for the connection from a customer
the samples were written for java 1.2, since the java 1.2 jsse raised an error while connecting to the proxy server (http1.1 instead of http1.0, so 200 connection successful was interpreted as an error), i changed to sources to run under java1.4, now it raises the http 403 error

sorry that i cannot describe it better, but as said i'm a newbie to java

any suggestions welcome

thanks,
big nell