OPC-DA AddGroup not working by using "TitaniumAS.Opc.Client" c# library - opc-da

Question

I'm getting a NULL reference error while adding the group. ie: in line -> opcDaGroup = server.AddGroup("Group");
Please help me out what's the issue and how to overcome the same.
whether this is the DCOM access issue.
Code:
public OpcDaGroup opcDaGroup;
private void StartConnection(string Cls_Id, string Machine_IpAddress)
{
try
{
log.Debug("START - Starting the connection");
Uri url = UrlBuilder.Build(Cls_Id, Machine_IpAddress);
server = new OpcDaServer(url);
server.Connect();
log.Debug("END - Starting the connection");
}
catch (Exception e)
{
log.Error("Could not connect to the OPC server for the IpAddress: {0}", e);
}
}
public OpcDaAdapterThreadImpl(string Cls_Id, string Machine_IpAddress, string name, ICollection<TagConfigurationModel> tags)
{
this.Cls_Id = Cls_Id;
this.Machine_IpAddress = Machine_IpAddress;
this.name = name;
this.AdapterReady = true;
Tags = tags;
var group = tags.GroupBy(c => new { ItemName = c.TagName }).Select(c => c.Key).Distinct();
grouptags = group.Select(c => new TagConfigurationModel { TagName = c.ItemName }).ToList();
opcTagItems = grouptags.Select(c => new OpcDaItemDefinition { ItemId = c.TagName, IsActive = true }).ToList();
// Connection Initializing
StartConnection(Cls_Id, Machine_IpAddress);
if (server.IsConnected)
{
// Add group to the server
opcDaGroup = server.AddGroup("Group");
opcDaGroup.IsActive = true;
// Add Items to group
opcDaGroup.AddItems(opcTagItems);
}
}