A com port error can arise when the default speed of a device is not set to the correct Baud or speed rate.
If you had to install a driver, or one provided to work with the telescope when connected to the pc.
It may have the option to set the baud rate.
This is the speed that data from the telescope can be sent to the computer, and vice versa if needed.
In order to make it work, you should have an option to select the Baud rate speed.
So the telescope should state its value of transmission.
If the the rate is set to high or low, then no handshake is made between the two devices.
You likely have to set the baud rate via the driver if one was required or installed, via a disk that came with the telescope.