I was getting the same message when using the Bluetooth panel to "Connect to serial port".
Now I do this:
1. Just pair the device but don't use the "Connect to serial port".
2. Then in a terminal type the command:
sudo rfcomm bind hci0 xx:xx:xx:xx:xx;xx
Where xx:xx:xx:xx:xx:xx:xx is the address for your device. You can see it in the Bluetooth panel.
You have to do it every time you restart.
I hope it works for you too.

Thanks, no dice.

I just don't know what is different for me than everyone else that gets this to work. Other than removing modemmanager after the install, my Raspberry Pi 3 is running a clean version of the Raspberry Pi 3 setup script found here.

I've tried having the rfcomm bind command in /etc/rc.local, and tried it without that. I've tried removing Blueman (a suggestion made here in this thread I think) and I've tried with Blueman installed.

I've tried manually trying to bind and connect via rfcomm. Nothing works.

I can kill VNC and disconnect from the RPI and immediately connect the mount in windows. I just don't understand it.

The steps I mentioned are in an old laptop using Ubuntu Mate 16.04.
I also have a StellarMate. Which uses a Raspberry Pi. On that one everything works. Probably because all the software was installed and tested at the factory. It also has Ububtu Mate 16.04. If you give up maybe you'd like to buy a StellarMate. They are not expensive and they ship them quickly.

The command for rc.local isI found no need to uninstall bluetooth manager, and you do have to make certain the dongle is paired.
Check that rfcomm0 is active withAnd make sure the INDI driver is set to connect to /dev/rfcomm0

You might also check and see what's using /dev/rfcomm0 for anything unexpected.Take the ID number
Don't give up yet. I went through all of this myself before discovering the conflict with modemmanager.

I removed and re-detected the bluetooth dongle via Blueman and paired it all over again. Here's what fuser and ps return, and this is the screen when I try to connect the mount. Same story every time.

scott@AstroPi:~/Desktop$ sudo fuser /dev/rfcomm0
/dev/rfcomm0: 10447
scott@AstroPi:~/Desktop$ ps -p 10447
PID TTY TIME CMD
10447 ? 00:00:00 indi_eqmod_tele

I'm not sure.
At this point I would recommend trying from a vanilla installation once more. Don't use the setup scripts. I have not used those and can not account for such variables.
Before anything else take these initial steps

• Install KStars, INDI-Full
• Remove modemmanager
• Pair, but don't connect the BT dongle with bluetoothmanager, or bluetoothctl
• Bind comm port to BT device in the terminal

  sudo rfcomm bind hci0 xx:xx:xx:xx:xx:xx 1

• Attempt to connect to EQMOD

Figured it couldn't hurt, it's only time. I did all that, and the same result. No matter what way I install things here's what happens:

I can pair the BT with the BT manager.
I can see that linux is recognizing the serial port I created (/dev/rfcomm0 created with either the rc.local setup or via command line) and that indi is controlling it when EKOS is running.
EKOS errors out when trying to connect to the port.

Every single time

I am sorry you are having so much difficulty.
Could you post some logs and a screenshot?

Here's a SS of it all in action. What logs would be good?

(EDIT) Here's the logfile from EKOS as well.

Did you remove modemmanager on this installation?

Yes. The only change made. Clean install, installed all relevant Indi/Kstars stuff, removed modemmanager. No script install on this one (although now I don't think that is the problem)