Steps:-
1] Log into the Azure site using partner credentials
2] Search and select Softchoice for hspl company
3] Now click on Invoice Management option from Benadmin curtain
4] Now edit an invoice in which only one month's invoice is generated.
5] Try to delete that invoice and observe

Actual Result:-
Server Error is displayed on click of delete button

Expected Result:-
Invoice should be deleted without any errors

Please let me know if you need any more information on this