If you go to make changes to one of your listings but cannot get into it (you get a message that the listing is currently being edit by someone else):
This means the listing has been locked for editing. This usually happens because the last person (list agent, admin, broker) to be in Add/Edit for that listing did not properly close the screen. They probably just clicked the X to close the window, or clicked a different tab to go to another part of Matrix.
If you do not use either the Submit Listing or Cancel Input buttons when you're were done on the input/change screen, Matrix will lock the listing and prevent it from being edited by any other users.
When this happens, the user who has the listing locked needs to go back into the listing through Add/Edit and then click the Cancel Input button. That will unlock the listing and allow it to be accessed by anyone with the appropriate privileges.