Like a1pha said, the certificate has expired that's all. For security purposes, browsers have to treat an expired cert like no cert. At the end of the day, it's your choice which site you visit, your browser is just warning you be default. Put simply, the cert is there for you, to ensure you are connecting to where you intend to be connecting.
You'll be able to change the setting on your browser, just have a quick Google specific to your browser. Sometimes, trying to explain certificates to clients is like pulling hen's teeth, it's hard for them to justify anything IT related if they can't see an instant and amazing benefit. Luckily Trav is an IT genius, so we don't have that problem.
Peace
Macre
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