It's been a long time since I owned a Celestron mount. If I remember correctly, there should be a "Virtual Comm Port" somewhere displayed on NexRemote, set it to any Comm port number that's not defined in your PC's device manager. And then set the same Virtual Comm Port number in your ASCOM driver. I am not sure if this will work because SGP didn't exists at the time I owned a Celestron mount. Try set it to COM5, COM6 or COM7.
SGP didn't exists back then but I was using Stellarium at the time and I needed to set the "Virtual Comm Port" number in NexRemote and set this same comm port number in Stellarium and it worked. It allowed me to control Celestron mount from Stellarium.
Since you already made NexRemote to work with your PC, this means you must have set the "real" comm port number in NexRemote to match the PC's hardware comm port number. Now, you need another comm port number for SGP to communicate with your Celestron mount via ASCOM driver which is why NexRemote added a "Virtual Comm Port".
Peter