Hello Pavan,
The error which you are facing, occurs because of duplicated entires in origanizationalentity table. If you have configured any databass with your jbpm engine, then you will have to check out the "origanizationalentity" table, in that table you may be having duplicate entries for User and Group,so you can remove one of the entries from the table.As i have mentioned that I had two entries for admin as a User and Group..
Regards
Irshad