We periodically receive bug reports that Sync Client was not able to connect to the server because of invalid SSL certificate. This is a rare error, but it continues repeating, so I decided to write a blog post about it.
Some new users may receive the following error when they start using MobileNoter Windows Sync Client:
System.ServiceModel.Security.SecurityNegotiationException: Could not establish trust relationship for the SSL/TLS secure channel with authority 'mobilenoter.com'. --->
System.Net.WebException: The underlying connection was closed: Could not establish trust relationship for the SSL/TLS secure channel. --->
System.Security.Authentication.AuthenticationException: The remote certificate is invalid according to the validation procedure.
This means that certificate that was issued for MobileNoter.com is invalid on your local machine. The reason it is invald is that Certification Authority that issued our certificate (GoDaddy) is not listed as Trusted Certificate Authority on your machine.
I'm not sure why this happens. GoDaddy are Trusted CA starting from 2004, and I believe they are being listed as Trusted CA in default Windows configuration for a long time. The only guess is that their certificate is removed either manually or by some software on particular machines.
To fix the problem, you have to install GoDaddy CA Root certificate.