Windows 8.1 upgrade fails on Inspiron 660

Attempting Windows 8.1 upgrade results in:

"We couldn't update the system reserved partition"

with event ID 20 from WindowsUpdateCilent for error 0xC1900104 when installing "English ESD bundle parent".

Googling this I find this is a problem for some systems with a system reserved partition that's 100 MB.

But, this machine with original Dell Win 8 install has nothing called that and no partition with that name or that small.  It has:

2 GB Recovery Partition
500MB EFI System partition
(the balance) OS partition
7.32GB Recovery partition

The EFI system partition is protected - I can't add a drive letter to it to see what's going on there.

I read and insured that the requirements of http://www.dell.com/support/Article/us/en/04/643934/EN were met. KB2871389 was listed as "failed" under update history, so I presume that means "not installed". Antivirus was disabled prior to starting the download.

Suggestions?