Function Designer Port Connection Failure

Hi... I'm connecting control modules in Function Designer. I'm having a problem trying to connect the output of one CM to the input of another CM, it looks fine in Function Designer, but when I go to generate the Control Builder diagram, I get an error about a port not being found. When I open the Control Builder diagram, the destination end of the connection is on a non-existing input port of the CM. I've inserted a screenshot below (I tried to attach the screenshot, the system wouldn't take it)

Any ideas why this is happening? I'm using PCDeviceLib CMs, the output and input ports are the same data type (PCC). There are other similar connections that seem to work fine in the same diagram.