When I am using SEPM plugin for Kaseya 2.5

Symantec™ Endpoint Protection Manager 12.1.4100
 Plug-in for Kaseya®   2.5
Error: Authorization Failed

An unexpected error has occurred during authentication. 
 
 
System.Net.WebException: The remote name could not be resolved: '<server name>' at System.Net.WebClient.DownloadDataInternal(Uri address, WebRequest& request) at System.Net.WebClient.DownloadString(Uri address) at System.Net.WebClient.DownloadString(String address) at SEPMWebServices.InteractiveAuthorization.GetAccessToken(NameValueCollection queryString) in c:\BBld_area\KaseyaPlugin_2.5\src\svn\source\SymantecWebServices\SEPMWebServices\SEPMWebServices\InteractiveAuthorization.cs:line 59 
 
Tried uninstall reinstall plugin again tried still not working any suggestion