I currently am unable to debug in GameMaker as it keeps saying "Unable to connect on port ####, please change value at General Settings->Debugging->Debugger Port" everytime I try launching the debug option.
I have tried changing ports and enabling real-time debugging. I also tried once disbaling the firewall thinking that was stopping the connection but to no avail. I am unsure as to why this is happening.
You may have windows firewall enabled, you need to disable it.