Error 8020 (error reading com device) occurs when driver for USB-to-serial adapter is not installed correctly or is not up to date.

Option 1: Contact manufacturer to obtain updated driver
Option 2: Purchase different USB-to-serial adapter with alternate driver

Note: For additional details, see Microsoft article PRB: MSComm.Input Returns comReadError (8020) with Some Serial Ports
Note: This problem is only know to occur with some third-party serial drivers