No luck, unfortunately, though the error is different, I've seen it before while testing this 4th axis. It gets beyond the onOpen section, but baulks at a later point:
Information: Configuration: Mach4Mill
Information: Vendor: Artsoft
Information: Posting intermediate data to 'C:\Users\User\Documents\GCode\1001.tap'
Information: Total number of warnings: 1
Error: Failed to post process. See below for details.
...
Code page changed to '1252 (ANSI - Latin I)'
Start time: Thursday, June 11, 2020 10:35:57 AM
Code page changed to '20127 (US-ASCII)'
Post processor engine: 4.5663.0
Configuration path: c:\users\user\appdata\roaming\autodesk\fusion 360 cam\posts\mach4mill.cps
Include paths: c:\users\user\appdata\roaming\autodesk\fusion 360 cam\posts
Configuration modification date: Thursday, June 11, 2020 10:30:27 AM
Output path: C:\Users\User\Documents\GCode\1001.tap
Checksum of intermediate NC data: 07209c62a06e8359e0f5498d7bd47548
Checksum of configuration: cc39f4d79fa1ca1e66c5dc12919c75f4
Vendor url:
http://www.machsupport.comLegal: Copyright (C) 2012-2020 by Autodesk, Inc.
Generated by: Fusion 360 CAM 2.0.8412
...
Warning: Work offset has not been specified. Using G54 as WCS.
###############################################################################
Error: Error: Section.getInitialToolAxisABC() is not allowed for section.
Error at line: 1
Error in operation: 'Rotary1'
Stack dump:
("Section.getInitialToolAxisABC() is not allowed for section.")@:0
defineWorkPlane([object Section],true)@c:\users\user\appdata\roaming\autodesk\fusion 360 cam\posts\mach4mill.cps:390
onSection()@c:\users\user\appdata\roaming\autodesk\fusion 360 cam\posts\mach4mill.cps:895
Failed while processing onSection() for record 343.
###############################################################################
Error: Failed to invoke function 'onSection'.
Error: Failed to invoke 'onSection' in the post configuration.
Error: Failed to execute configuration.
Stop time: Thursday, June 11, 2020 10:35:58 AM
Post processing failed.