When a design is locked then selected, a lock icon is shown in the Design tab in Workflow Manager. There are several reasons for a locked design, which are described here: http://resources.arcfmsolution.com/10.2.1c/DesktopUsing/LockedDesigns.html.
Occasionally, the Unlock task will not work to unlock the design. If this occurs, click on the lock icon, which writes an Info event to the Miner event log. The event will include the reason for the lock to aid in further troubleshooting.
In this example the design is locked even though the login user is kevin, the owner is kevin, and it is in a state (In Design) that should allow editing. Clicking on the lock icon writes this event to the Miner event log:
This shows that the design is locked due to the LOCKED field being set to -1 for this design in the PROCESS.MM_PX_CURRENT_STATE table. This happens when ArcMap crashes or loses its network connection. If the Unlock task does not work for some reason, the LOCKED field can be manually set back to 0 by utilizing SQL statements.