You and other user logged into your account at the same time and tried to modify from both side.Please refer the below link for further information.
https://community.intuit.com/questions/1177245-error-message-you-and-another-user-were-working-on-this-at-the-same-time-the-other-user-finished-before-you-did-so-your-work-was-not-saved
