This applies only when the user is manually instantiating the stratixv_mac component (i.e. WYSIWYG flow).
You will get the above error if the "chainin" port is present on the stratixv_mac instantiation, but it is not connected to the chainout port of another DSP block. You may also get this error if the "use_chainadder" generic is "true" when the chainin port is not being used.
Quartus is expecting the chainin port to be either disconnected (not present), or connected to the chainout of another DSP block. Connecting chainin to a fixed value (0, 1, X, Z) does not count as being disconnected. Quartus also expects "use_chainadder" to be "false" if chainin is not used.
To resolve this issue, either disconnect the chainin port entirely and set use_chainadder="false".