Hi Matthew,
The "Port 1" referenced in the error message is the first output port, not the input port. All output ports from the If block have to feed If-Action subsytems, and the outputs of those have go through a Merge block. The If and If-Action blocks implement this pseudocode:
IF cond1 Then
Action1
ElseIF cond2 Then
Action 2
Etc.
Else
ActionElse
EndIF
The model in the Question is missing the Action for the conditions.
I think the model was trying to implement functionality similar to this model:
Here, the top If-Action system outputs 1 and the bottom outputs -1. The If-Action subsystems can also accept inputs.
Of course, this model could be more easily implemented by sending the output of the Sine block into a Sign block, but I thought it would be worthwhile to illustrate how the If/If-Action works.
