Invalid Certificate?

[Aliceacc]

Every once I a while, I get a pop up saying that the Disboards has an invalid certificate (I think that's the phrasing) and that it would be dangerous to proceed.

I try to override, but it invariably doesn't let me. I end up restarting the computer and going to another site.

It's only the Disboards, and it's on both my computer and my husband's.

Any idea how I can fix this?