The NS, #20 error message displays the following warning:
An attempt was made to form a connection of more than 64 members that used acknowledged service or polling.
Only unacknowledged or unacknowledged repeated services are allowed for connections with more than 64 members.
The error message is fairly self explanatory. LNS connection tools do not permit creating connections between more than 64 devices where the connection service uses Acknowledged service. The protocol supports this type of connection and service but LNS tools do not. The connections in the Visio drawing may look as if repeated service type is used. However you can still create a group connection if you are trying to connect to an input network variable and the code in the receiving device declares the variable as using the "polled" keyword. This means that a group connection is made in reverse. The drawing may look like it is a fan in connection from 63 other devices to the input network variable which is the 64th device but the fact that the input variable polls all the other 63 output network variables, creates the group.
The Visio drawing may show that repeated service is used before a binding but that may be because the connection uses an alias. After attempting to delete the connection the alias is no longer used and the goup ackd connection is made.