Error on Inventory lookup manual search of item: Value cannot be null

I am trying to search an item  inventory by giving Item number in Inventory lookup option on Retail POS, event viewer showing error-'Microsoft.Dynamics.Retail.Pos.Dialog.WinFormsTouch.formInventoryLookup, Text: Inventory lookup: System.ArgumentNullException: Value cannot be null. Parameter name: host at Microsoft.Dynamics.Retail.TransactionServices.ClientProxy.TransactionServiceClientFactory.BuildTransactionServiceAddress(String protocol, String host, Int32 port, String serviceName, String serviceArea) at Microsoft.Dynamics.Retail.TransactionServices.ClientProxy.TransactionServiceClientFactory.GetEndPointAddress(String serviceArea) at LSRetailPosis.TransactionServiceClientFactory.CreateTransactionServicePOSClient() at LSRetailPosis.TransactionServices.CheckConnection().'

Any pointers why this error is coming and how can it be rectified? is it related with Real time sync service?