If you are not getting the Gnutella OK then the particular connection needed to succeed is not making it. There can be several reasons.

- Are you running any firewall software
- Do you have a hardware firewall
- If you are on an academic or Business LAN is your system administrator blocking traffic on port 6346.
- If you are using a public ISP is your ISP blocking traffic on port 6346.

Since you know of another pserson on the same ISP is OK it is still possible that a given router withing your ISP is blocking you and the other person may not be going through the same path... I think a phone call to your ISP would be in order.