I also found that it always helps to open SmartSDR CAT and refresh its port list so I can observe which ports are open and whether or not they are dedicated or shared. As I get older and more "seasoned" it helps to have these visual reminders, because I can't remember any more!
For most of the simple Digi modes, I have found that FlDigi was easier to use than HRD. ..... so far.....
BTW> In setting up FlDigi, I found about three of four different places where I had to go in and select the sampling rate of 48000 (in the sound card set up, and at least two places in the windows control panel>sound devices> properties, etc) in both the RX and TX paths. I was getting some higher IMD on PSK31 before I rechecked all of the settings. I had thought I had gotten them all, but apparently I had missed one!
Kirk: This is possibly late to help. However, Each Time I start Fldigi, I have to Open the Fldigi configuration window and initialize the Hardware PTT, reload the SmartSDR.xmj file and initialize both before SmartCAT or DAX works correctly. The necessary boxes in Fldigi configuration are checked and each new Fldigi configuration is saved after changes are made. This configuration process has to be repeated each time Fldigi is started, because the Fldigi configuration is not saving the new settings..
Honestly, this is horrible quality engineering for a program that does not interface with the radio and Smart SDR. This is not even beta quality work. I've wasted two hours trying to get CAT to transmit again. I've done everything by the letter and it no longer works. You talk about horrible engineering, this is it! Shame on you guys.