以下摘自ICQ官方的help：

Q.
When trying to send a file, ICQ gives me a "Can't Establish Direct Connection" error message, what can I do?

A.
Note that the file transfer uses a direct peer-to-peer connection. There are many reasons why this sort of connection may fail, including:
The path between the two computers is incorrect.
A failure in one of the routers between you and the other party.
A firewall from your end or the other end that disrupts the connection.
You may wish to check if either party's connection is restricted by a firewall. For more information on firewalls, refer to our Firewall Center