When I load the login page, my Firefox does not object: https://www.marykayintouch.nl/Login/Login.aspx

Is this the only site that is giving you a certificate error or have you gotten errors on numerous HTTPS sites?

If it's just this site

When you have a problem with one particular site, a good "first thing to try" is clearing your Firefox cache and deleting your saved cookies for the site.

(1) Clear Firefox's Cache

See: How to clear the Firefox cache

If you have a large hard drive, this might take a few minutes.

(2) Remove the site's cookies (save any pending work first). While viewing a page on the site, try either:

• right-click and choose View Page Info > Security > "View Cookies"
• (menu bar) Tools > Page Info > Security > "View Cookies"
• click the padlock or globe icon in the address bar > More Information > "View Cookies"

In the dialog that opens, you can remove the site's cookies individually.

Then try reloading the page. Does that help?

If multiple secure sites are affected

When you get this for pretty much all secure sites, the problem usually is one of the following:

(1) Error in your system's date, time, or time zone, which throws off certificate validity checks. Sometimes allowing computers to use an internet-based time source can introduce this problem.

(2) Firefox not being set up to work with your security software that intercepts and filters secure connections. Products with this feature include Avast, BitDefender, ESET, and Kaspersky; AVG has a Search Shield feature which can cause this error on search sites.

(3) On Windows 10, Firefox not being set up to work with the parental control software Microsoft Family Safety.

(4) Malware on your system intercepting secure connections.

So... which is it?

If you have any of those specific security products, that would be the first thing to check. We might be able to assist with specific next steps based on what you have if you tell us.

Otherwise, we could suggest methods of investigating the certificate further.

I cleared my cache and my cookies. Whatever device I use within this network cant get acces. So it may not be a problem of the site owner but within my own system. I have this problem only with this website. Any other site I can get acces to. this problem happened overnight I cannot find the solution yet. I also traced it with a cmd.

kulsters said

Whatever device I use within this network cant get access.

Perhaps there is a DNS problem with your network router/gateway/firewall. If you check the address from within your network, do you get unusual results? For example:

in a cmd.exe window:

C:\nslookup www.marykayintouch.nl

Non-authoritative answer: Name: www.marykayintouch.nl Address: 185.49.172.91

That IP address is part of a block (185.49.172.0 - 185.49.175.255) registered under "Pink Rose Information System Services Ltd." in the U.K. with a contact address in Dallas, TX.

how can I remove that block? (the contactadress in Dallas is the worldwide headoffice.)

I don't know why you have this problem, so it's too soon for me to suggest a solution.

Could you try the nslookup from a command window and see what result you get?