I’m upgrading from 2024 R1 to 2024 R2. ERP installation goes fine, and the database upgrade completes successfully. However, the site upgrade fails.

Full text from the window is here -
Exception occurred while updating the site files.
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Inner Exception:
Exception occurred while backing up the files from 'C:\Acumatica\Program Files\Instance\AcumaticaDB2023R1\' directory. Try to do it manually.
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Inner Exception:
Could not find a part of the path 'C:\Acumatica\Program Files\Acumatica ERP\BackUp\Sites\AcumaticaDB2023R1_20241010_173255.zip'.
This looks like some sort of permissions error, but I’m just guessing. I am an domain admin, domain account explicitly in the Administrators group on the server, and has Full Control in Windows permissions. I don’t know if it’s my credentials used when the site is updated, or if it’s an Acumatica or IIS user.
I have restored my VM back to the point before I started the ERP installation.
Thanks in advance for any ideas on how to fix this.