Error while opening POS

Hi,

I am facing issue while opening POS, following error is loged in event viewer

LSRetailPosis.POS.Program: LSRetailPosis.PosisException —> System.NullReferenceException: Object reference not set to an instance of an object.
at Microsoft.Dynamics.Retail.Pos.DataManager.CustomerDataManager.ConvertToTransactionalCustomer(Customer axCustomer)
at LSRetailPosis.BusinessLogic.CustomerSystem.GetCustomerInfo(String customerId)
at Microsoft.Dynamics.Retail.Pos.Tax.TaxEngine.TaxEngineServiceProxy…ctor(IApplication application)
at Microsoft.Dynamics.Retail.Pos.TaxService.Tax.Initialize()
at Microsoft.Dynamics.Retail.Pos.SystemCore.Services.Initialize()
at Microsoft.Dynamics.Retail.Pos.SystemCore.PosApplication.Initialize()
— End of inner exception stack trace —
at Microsoft.Dynamics.Retail.Pos.SystemCore.PosApplication.Initialize()
at LSRetailPosis.POS.Program.InitializeAndLoadPOS(String[] args, Boolean owned, SplashScreenForm splashScreenForm)
at LSRetailPosis.POS.Program.Main(String[] args).

Kernel version:6.3.6000.214

Application version:6.3.5000.133

GST has been already installed on the same.