When trying to upgrade ESXi 5 I got an error about altbootbank

When trying to upgrade an ESXi 5 host with VMware Update Manager, I got the following error:

There was an error checking file system on altbootbank, please see log for detail.

Related tags: VMware

cd /dev/disks

You should see stuff similar to this in that directory:

These are all individual partitions on the disk. I was unable to find a way to map the partition to /altbootbank, but I found that if I ran:
dosfsck -v -r naa.600508e0000000006c35e1f61ecd8f01:1
On each one I eventually found one that had errors:
Reclaimed 4 unused clusters (16384 bytes).
Perform changes ? (y/n) y
naa.600508e0000000006c35e1f61ecd8f01:5: 17 files, 25403/63929 clusters

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