|It seems the issue is with FTP or port 21 on L, both listening and trying to establish a connection to another server. |
What are the error messages, if any, you receive on L and B when trying to establish FTP connections?
The fact that none of the computers can ping each other is strange. You mention the firewall being turned off on all three, however, is there are kind of security software (Norton, AVG...) on L that may be interfering with this connection?
Can A access the FTP server on L? And can L access the FTP server on A?