Which version you are using ? if you are using 7.0.1 or 7.0.0 try with workaround provided in jira [RHPAM-1250] [GSS](7.0.x) Recurring error: An error has occurred while trying to lock this asset - Red Hat Issue Tracker
Thank you, Abhijit.
It was 7.28.0. It was hopeless case and I had no time to waste so I switched to 7.31.0 instead. That one has no "trying to lock this asset" issues but something completely different. What a lovely piece of tool! Every single time you click on a Human Task it complains politely. You can choose how frequently you want to be reminded that you have an error, however.