Why does Online Store appear as "Closed for Maintenance"?

The Online Store has a feature which allows you to take your store offline for maintenance:

1. In the Sitebuilder, go to Menu > Store.
2. Go to Settings > General.
3. Click Store Profile.
4. Click the Close Storefront Maintenance button.
5. The Store widget on your site will display a "This store is closed for maintenance" message.

This feature can also be inadvertently activated in your account. To reverse this action, do the following:

1. In the Sitebuilder, go to Menu > Store.
2. Go to Settings > General.
3. Click Store Profile.
4. Next to the "Storefront is Closed" message, click Open Storefront.
5. Your store will now be available again.