I am very green when it comes to this type of problem so would appreciate it if there is a solution to the problem it could be explained in lay mans terms.
Do you receive the same error using IE, Chrome and Firefox (IE and Chrome use the Windows Trusted Root CA directory and Firefox uses its own directory)?. An screenshot with the error could help.
Just for the records, https://letsencrypt.org doesn't use a certificate issued by Let's Encrypt.
Are you using a proxy?. Do you have some kind of antivirus?. Some of them act as a proxy performing some kind of man in the middle intercepting these connections. I you are using one... disable it completely and try again.
Time to sleep here but if you can answer the questions some community's member could follow the issue and try to help you to solve it.
Root CA issuers are different, both belong to IdenTrust but are different (IdenTrust Commercial Root CA 1 vs DST Root CA X3). Even if no Root CA certificate for IdenTrust was there, Let's Encrypt certificates could still work if the ISRG Root CA Certificate is installed properly .
Many thanks for your replies. to answer some questions
Tried access with Firefox and find no problem - IE still has problem
Windows up dates are all up to date - last one loaded yesterday
Using Avast but removed it yesterday and problem still with IE
Also turned off firewall - same problem
After further investigation I was able to access the Certification path and find that the problem sites
are:-
DST Root CAX3 - IdenTrustCommercial Root Ca 1 - TrustID Server CA A52 - letsencrypt .org
& DST Root CAX3 - Let’s Encrypt Authority X3 - www.beiley.com
When I highlight the DST Root CAX3 the certificate status box says - The CA Root certificate is not trusted because it is not in the Trusted Root Certificate Authorities store.
This would obviously seen to be the problem as when I check -Trusted Root Certification Authorities - certificates - I cannot find DST Root CAX3 mentioned.
My question now is how do I get DST Root CAX3 registered as a trusted Certificate - is it possible to copy the file from my Win 10 Machine to Win 7 machine - will it work or do I need a Win7 version.