Upgrade from 11.3-U5 to 12 failing

[Jestocost]

Hello,
I am trying to upgrade from 11.3-U5 to 12 and it fails at 66.67% with the following error message after about 3 minutes.
Error: Cannot remove package base-os if it still has files.

Any help would be appreciated.

Thank you,
David Brown

System Info
Version - FreeNAS-11.3-U5
Mother Board - MSI MS-7693
CPU Athlon 6 core
Memory 8 GB
On board network and SATA controllers
Boot drive Crucial - C300-CTFDDAC064MAG
RAIDZ1
Seagate - ST33000651NS 2.73 TB
Western Digital - WDC WD30EFRX-68AX9N0
Western Digital - WDC WD30EFRX-68AX9N0
Western Digital - WDC WD30EFRX-68AX9N0