SeaMonkey version 2.49.3 Browser won't load Google and youtube sites

[dirk]

I recently installed SeaMonkey version 2.49.3, but thr browser won't 
load Google and youtube sites, saying it is not safe....

the error is
<a 
id="errorCode"title="SEC_ERROR_UNKNOWN_ISSUER">SEC_ERROR_UNKNOWN_ISSUER</a>

Do I need a certificate to download?
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