Shared workbook

Hello, I have a couple of Excel Trackers on a Drop Box shared drive. For some reason I cannot get them to be shared but only allow one user to edit at a time. Usually if someone is in edit mode on a shared spreadsheet another user will get a notification for read only as it is locked for editing by another user. 

Maybe its the new excel but I cannot seem to get the trackers to this point.

Anyone know what I am doing wrong or not doing?

Thank you