Hello Ying,
This is common error when your CVC is locked which is preventing ATP Check. Many time retrying the ATP Check can also solve this locking issue.
Yes, Lock entries can be deleted using SM12 or RS12. I will suggest, please check Tcode. SM04 to know the list of users currently in the system and what transaction they are using etc. If you blindly delete any lock entries from SM12, it may create a problem/inconsistency with the data. Details from SM04 will help you avoid deletion of genuine lock entry from SM12.
Hope this will help.
Thank you
Satish Waghmare