Cannot update to latest update of High Sierra - NSURLErrorDomain error -1012

Hi,

I cannot seem to update my OS X - High sierra 10.13.5. on a Retina, 15-inch, Mid 2014 Mac Book Pro)
I receive the following error when I check for updates in the App Store on the MBP:

"The operation couldn’t be completed. (NSURLErrorDomain error -1012.)"

I have also changed my password to my gmail account and cannot enter the password either on my mac book pro or on my iPhone 7Plus

I am wondering if my certificates have been deleted. I do have recent time machine backups available but do not know how to restore certificates....

I enabled keychain on iCloud with no password an hour ago to see if this would help. But it didn't. Entering safe mode also did not work.

Thanks for your help.

David