The Certification Authority is not trusted because it is not in
the Trusted Root Certification Authorities store. This commonly
occurs if your organisation issues your own SSL certificates, for
example using SelfSSL in a development/testing environment.
Note - You may not receive an error while browsing to the site
using I.E. if you or your network administrator has setup the
internal Certification Authority to be trusted either for your
profile or on your local machine, but has not added the CA
Certificate to the servers certificate store.
A SSL certificate is only valid for a particular
name, or if a wildcard certificate is used, a particular domain.
Check that the certificate is valid for the address that is listed
in the error message - you can use IE to test this.
Note that a SSL certificate will be valid for a FQDN
such as sharepoint.mycompany.com but will not be valid for the IP
address that this maps to. This means that if you access the site
using the IP address you will receive this error.
If you notice that an IP address or incorrect URL is listed in the
error message then you have not set SecureBindings in the IIS metabase. This is similar to the DNS Alias
problem as without the SecureBindings property being set SharePoint
has no way of determining the DNS name that an IP address
represents. You will also notice that SharePoint Administration
pages Virtual Server List shows the sites by their IP address or
incorrect URL.
To correct this follow the steps listed here to set
the SecureBindings metabase property
cscript.exe C:\Inetpub\AdminScripts\adsutil.vbs set
/w3svc/<site identifier>/SecureBindings ":443:<host header>"
http://www.microsoft.com/technet/prodtechnol/WindowsServer2003/Library/IIS/8d9f2a8f-cd23-448c-b2c7-f4e87b9e2d2c.mspx
Where <hostheader> is the host header for the site
and the <site identifier> is IIS's internal Site ID.