Job cancelled_Message No. MC601

Hello experts,

There is a background job (program RVKRED77) scheduled every day at 4AM. In the recent 2 weeks, the job is cancelled because the same user locked the object. The user said he had logged off SAP and worked since 8AM. I checked that yesterday via SM04 and this user ID did not show. However, same issue happened today.

Pls advise. Thanks.