When I select File>Edit Printer Driver Configuration to edit any of my *.pltcfg plot driver files, the file is being edited by the Windows Notepad utility instead of the usual MicroStation XML editor. If I select a *.plt file to edit, Notepad is the default editor as it should be.
Discovered that the MS_PLTFILE_EDITOR variable had be set to NOTEPAD.EXE. The default value is [Undefined]. When undefined (blank), the MicroStation XML editor is used for *.pltcfg Printer Driver Configuration files and Notepad is used for *.plt plot drivers. Removing the NOTEPAD.EXE entry for this variable corrected the problem.