Cannot connect to particular server

Hi all got a crisis and would appreciate very much if i can get some help

We try to connect to our server using SmartFTP from our work computer (or any on the same network) we cannot connect.

We can connect to the SAME server from home or another network

we can conect to a DIFFERENT server, any found in the the SMARTFTP favorites, for example.

At first i thought it may be SMARTFTP but when we tried to connect using another FTP client the same prob occurred

Socket connected waiting for login sequence.
Connection timeout. No response from server.
Cannot login waiting to retry (30s)...


The network admninistrator has no idea why it will block one IP and not any others....
would appreciate some help thy very much


Alex