Our Salesforce instance is making an outbound call to a web service and receiving the following error:

IO Exception: sun.security.validator.ValidatorException: PKIX path validation failed: java.security.cert.CertPathValidatorException: Usage constraint TLSServer check failed: SHA1 used with certificate: CN=Thawte SSL CA, O="Thawte, Inc.", C=US. Usage was tls server

The call to this web service has been working fine up until Monday of this week. The certificate the server is using is present on the list of certificates trusted by Salesforce and specifies that is uses SHA1 and not SHA256:
https://developer.salesforce.com/page/Outbound_Messaging_SSL_CA_Certificates#thawteprimaryrootca

Anybody else experience an issue like this? This is not 2-way SSL so there is no certificate on the Salesforce side. Salesforce is usually very good about announcing security updates/changes so it seems weird that this would just stop working all of a sudden.

I can no longer login to two sandboxes (Full-copy/developer) after refreshing them from a production environment. I can login to each site through a browser without any issue. I can also login through the AJAX Toolkit Shell without any issues. the I tried resetting my password in one of them and still no luck. No combination of password/security token works either. The same is true for the Data Loader. 

I can no longer login to two sandboxes (Full-copy/developer) after refreshing them from a production environment. I can login to each site through a browser without any issue. I can also login through the AJAX Toolkit Shell without any issues. the I tried resetting my password in one of them and still no luck. No combination of password/security token works either. The same is true for the Data Loader.