When I implement or synthesize a schematic design, the following message occurs:
"ERROR:DesignEntry:206 - Net <net_name> must be connected to a symbol pin or an I/O marker."
This is a valid error, and it occurs when a net is left floating on both ends and needs to be connected to a symbol pin or an I/O marker.
To remove this message, connect the net to a symbol pin or an I/O marker.
In ISE 10.1 and later, the net may be left floating if the user does the following to change this error to a warning message:
1. Select Edit -> Preferences -> Schematic Editor -> Check.
2. Change the value of both "Consider Loadless Nets and IO as" and "Consider Sourceless Nets and IO as" to Warning.