When detailing down into a form or screen, the resources used are locked. If you do not log out of Colleague (e.g. you close the window without clicking log out), the resource will remain locked for anywhere from 15 to 30 minutes before the session or lock expires. This can also happen if there is a SQL or Colleague script error that interrupts a save. You can use LRCS to unlock users, forms, and screens.
For more information, including the SQL query to investigate and unlock, see Ellucian Hub Article #000005834.