The socket closed may usually occur due to issue in LDAP Server itself.
It could be a timeout from LDAP Server. So, I would cross verify the same by trying to connect the LDAP Server through external client tool like Active Directory Explorer.
If there is no abnormality or issues in my source LDAP Server then I will try to do the below configuration changes in Denodo platform to see if that works.
* Make sure the Enable Connection Pool checkbox is selected in the configuration section of LDAP datasource in Denodo.
* If the connection pool enablement does not help, Would try to increase the connection timeout value for LDAP Connection Pool in VDBConfiguration.properties file present in <DENODO_HOME>\conf\vdp folder.
> #LDAP - Connection Pool
The above default connectionTimeout in the properties file can be increased.
* Make sure to stop the Denodo server before changing the above .properties file.
* After saving the changes, restart the Virtual DataPort Server.
I would go through [**LDAP Sources**](https://community.denodo.com/docs/html/browse/7.0/vdp/administration/creating_data_sources_and_base_views/ldap_sources/ldap_sources#ldap-sources) section of Virtual DataPort Administration Guide to get more details on LDAP datasource connection.
With respect to Active Directory Explorer testing, I would use [**this**](https://docs.microsoft.com/en-us/sysinternals/downloads/adexplorer) link to download. While configuring connection, provide the <HOSTNAME>:<PORT> along with proper credentials for LDAP datasource.
Hope this helps!