ITAB_DUPLICATE_KEY

Hello Experts,

I hope you are well.I got a error when save my sales order through VA02.When I am going change my sales order and save and then click on back button,then the error is occurred.Then I got mail in my SBWP mail box.

Below mail received.

Update was canceled

System ID.... HMP
Client....... 200
User..... INFOCUS
Transaction.. VA02
Update key... EF09C90A692A00F0E005B9010618BF15
Created...... 18.09.2018, 15:58:53
Completed.... 18.09.2018, 15:58:53
Error Info... Internal session terminated with a runtime error ITAB_DUPLICATE_KEY (see ST22)

Also attached the dump detail.Please help me out.