Error when trying to select customer in AX 2012 R2 POS

Need help. Thank you in advance.

Here is the complete error message in the event viewer.

LSRetailPosis.POSProcesses.CustomerSearch: System.InvalidOperationException: Sequence contains more than one element
at System.Linq.Enumerable.SingleOrDefault[TSource](IEnumerable`1 source)
at System.Data.Objects.ELinq.ObjectQueryProvider.<>c__11`1.<GetElementFunction>b__11_2(IEnumerable`1 sequence)
at System.Data.Objects.ELinq.ObjectQueryProvider.ExecuteSingle[TResult](IEnumerable`1 query, Expression queryRoot)
at System.Data.Objects.ELinq.ObjectQueryProvider.System.Linq.IQueryProvider.Execute[S](Expression expression)
at System.Data.Entity.Internal.Linq.DbQueryProvider.Execute[TResult](Expression expression)
at System.Linq.Queryable.SingleOrDefault[TSource](IQueryable`1 source)
at Microsoft.Dynamics.Retail.Pos.DataManager.CustomerDataManager.GetElectronicAddressesForLocation(Int64 locationId)
at Microsoft.Dynamics.Retail.Pos.DataManager.CustomerDataManager.SetCustomerPostalAddress(Customer customer, PostalAddress postalAddress)
at Microsoft.Dynamics.Retail.Pos.DataManager.CustomerDataManager.GetTransactionalCustomer(String accountNumber)
at LSRetailPosis.BusinessLogic.CustomerSystem.GetCustomerInfo(String customerId)
at Microsoft.Dynamics.Retail.Pos.Customer.Customer.Search()
at Microsoft.Dynamics.Retail.Pos.Customer.Customer.Search(IPosTransaction posTransaction)
at LSRetailPosis.POSProcesses.CustomerSearch.Execute().