Curl Error: Couldn't resolve host 'f'

When I check the update page in Sysadmin - View Log, I am consistently see the following messages:

2017-03-03 07:12:13: (0) Requesting updates
2017-03-03 07:12:13: (0) Error acquiring update
2017-03-03 07:12:13: (0) curl Error: Couldn’t resolve host 'f’
2017-03-05 07:12:13: (0) Update already in progress (locked)
2017-03-08 07:12:12: (0) Update already in progress (locked)
2017-03-10 07:12:13: (0) Update already in progress (locked)
2017-03-11 07:12:13: (0) Requesting updates
2017-03-11 07:12:13: (0) Error acquiring update
2017-03-11 07:12:13: (0) curl Error: Couldn’t resolve host 'f’
2017-03-16 07:12:12: (0) Update already in progress (locked)
2017-03-17 07:12:14: (0) Update already in progress (locked)

I have used “usr/sbin/sysadmin_update_system --unlock” but with no success. Anyway the system is saying no updates required so I am assuming that it is failing to pick up any updates.
I am currently using 10.13.66-19

Can anyone advise how I can fix "curl Error: Couldn’t resolve host ‘f’ "?

Thanks for any help.
Regards