I had an issue when using update manager to scan a host and it would fail with a “Check log for errors blah blah blah”. The errors are never useful. After investigating and checking the log, I found the following entry:
2015-06-02T20:57:30.312-07:00 [00504 info ‘VcIntegrity’] Error on logout (ignored): vim.fault.NotAuthenticated
When researching the issue, I came across a best practices guide that basically pointed out the error. So as a general best practice, verify on your hosts, on the configuration tab, under DNS and Routing, that you have filled in all the fields. I had missed the Search Domain field on that particular host which was causing the scan to fail.
The fields with the blue boxes will cause the Update Manager scan failure as well as cause other issues with DNS on the host. Just another one of things to check!
As always, leave questions or suggestions in the comments.