You will see this error when an attempt is made to exceed the limit of 3 concurrent FTP connections to a hosting package. 

Some FTP clients are set up by default to make numerous connections at once in an effort to increase transfer speed. In reality, this results in only a marginal increase in speed, and a considerable degradation of server performance. 

If you are using an FTP client, there should be an option to set the number of simultaneous connections that can be made to the server â€“ please ensure that this is set to a maximum of three. Additionally, ensure that no other computers are connected to the server, as each connection will count towards the limit.