Problem Logging into Bigcommerce Storefront

This morning I tried to login to my Bigcommerce storefront to process my orders. I followed the proper link (same as I always do), but a page comes up that says:

There is a problem with this website's security certificate.

The security certificate presented by this website was issued for a different website's address.

Security certificate problems may indicate an attempt to fool you or intercept any data you send to the server.
We recommend that you close this webpage and do not continue to this website.

What is this? I can't login.