This fix for this is quite simple and can be used until Blizzard releases an update.

Within the launcher, under the ‘PLAY’ button, change the server to your non-primary region

Then select ‘options’-‘check for updates’

After the launcher updates your non-primary region, exit and re-open, selecting your primary region. The game should be fully updated and launch from there.

This bug has turned up on occasion ever since the beta version, and still seems to pop up here and there on patch days.

Blizzard announced they will be performing maintenance Tuesday morning that might effect logins. This could be an attempt to fix the current ‘versions’ error. Be patient with the maintenance and make sure to follow @BlizzardCS for updates.