You should review the server logs to get more information about this error.
Could you please provide us the complete error log. Also make sure to import salesforce certificate in to server.
There could be multiple reason of this error. Actual cause can be found at server detail logging. Reason could be - 1. credentials are not correct 2. certificate (*.Salesforce.com) has to imported into weblogic server 3. if you are not ale to access Salesforce.com from domain you are in (HOST_NOT_FOUND) Please provide more details on this, I certainly should be able to help you.