DB2 10.5 - When inserting, the database is trying to reuse index keys on GENERATE ALWAYS
Determine the largest current ID value:

select max(TIMESHEET_ID) from PROJECTMGMT.TIMESHEET


then reset the identity value:

alter table PROJECTMGMT.TIMESHEET 
  alter column TIMESHEET_ID restart with &lt;whatever the max value is + 1&gt;