This can be caused by an old version of Secure Node that may have previously been installed. Look in the sslexplorer/conf/repository/archives directory for a file called sslexplorer-enterprise-secure-node.zip and delete it if it exists.

 Restart the SSL-Explorer service and see if the error disappears. If it has and you need to use Secure Nodes, then you can reinstall it from the Extension Manager.

 Please see the related article regarding Secure Nodes not connection with 1.0.1.