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TLS Error 75777 - Unexpected Message Received

 

The most common cause of TLS error 75777 (ERROR_SSL_UNEXPECTED_MESSAGE) is a transparent proxy. A transparent proxy is a proxy that does not need to be explicitly set. Instead, certain connections are automatically handled by the proxy. For example, if a connection is established via port 80, it is automatically accepted by the (HTTP) proxy, since it is assumed that a connection to a web server is to be established. However, if no HTTP connection is to be established over port 80 at all - for example when checking licenses over port 80 - this TLS error occurs: The proxy accepts the connection and responds with an HTTP header, but !MC5 expects a TLS message.

 

In case of this error, check that no transparent proxy is used in your network. If this error occurs during the license check, change the port of the license check to 8920 instead of 80. This should fix the problem. However, you may still need to release port 8920 in your firewall.