Upgrade error...database has no user?!

I have automatic upgrades turned on for my WordPress install, which has worked fine in the fast but last night I got the following error message email when apparently an upgrade to 3.9 was attempted:

[b]We were unable to set up wordpress as requested at:
(My website)

The problem was Invalid DB User: your database (website database) has no user and we couldn’t safely update!

Please correct this and go to our web panel and re-submit your
wordpress upgrade request.[/b]

I’m confused as the website is working fine, I’ve checked on the MySql Databases page on my panel and users are there and defined, and I also see the correct user if I look in the wp-config.php file.

Anyone have any idea what could be wrong and where I should check? (Please note that I am far from an expert on these things but can troubleshoot some things if explained simply…)

What’s your domain? I can take a look for you.

Thank you if you can look into it!