You can't start a WO right now because you already have a WO on your device that has been started. Work Manager tracks some additional status values as user status and mobile status values. Your screen shots are not very clear so I can't say for sure but it looks like the third work order in your list is already started. You can tell by the icon in the list. If you select that WO you will be able to put it on hold or complete it and then you can start another WO.
--Bill