What works for me is adding the serial printer as if it were a network printer, e.g. choosing "LPD/LPR-Host" or "Internet Printing Protocol (ipp)" and then entering as URL the path to the device, e.g.:
or in my case, using a serial to USB adapter:
You can see which device the printer is attached ...
I would like to add an alternate answer to this similar symptoms: when everything is installed correctly and nevertheless the "Error during read: Error during device I/O error" or "Device is busy" came.
To me it happened with a network all in one Canon MF8200C and the answer is that the machine is not getting automatically in scan mode. One need to enter ...