Object reference not set to an instance of an object

Dear All,

Tried to start work period and i got this error.
Please kindly assist me.

[General Info]

Application: SambaPOS
Version: 4.1.82
Region: en
DB: SQ
Machine: CHD8700
User: CHD8700A
Date: 9/18/2018
Time: 10:39 AM

User Explanation:

CHD8700A said “”

[Exception Info 1]

Top-level Exception
Type: System.NullReferenceException
Message: Object reference not set to an instance of an object.
Source: Samba.Presentation.Services
Stack Trace: at Samba.Presentation.Services.Implementations.InventoryModule.SaleReader.GetSaleTransactions(List1 orders) at Samba.Presentation.Services.Implementations.InventoryModule.SaleReader.Read(IEnumerable1 tickets)
at Samba.Presentation.Services.Implementations.InventoryModule.CostCalculator.Calculate(IList`1 tickets)
at Samba.Presentation.Services.Implementations.InventoryModule.InventoryService.CalculateCost(PeriodicConsumption pc, WorkPeriod workPeriod)
at Samba.Presentation.Services.Implementations.InventoryModule.InventoryService.UpdatePeriodicConsumptionCost()
at Samba.Presentation.Services.Implementations.InventoryModule.InventoryService.DoWorkPeriodStart()
at Samba.Presentation.Services.Implementations.InventoryModule.InventoryWorkperiodProcessor.ProcessWorkPeriodStart(WorkPeriod workPeriod)
at Samba.Presentation.Services.Implementations.WorkPeriodModule.WorkPeriodService.StartWorkPeriod(String description)