InCopy error when opening files through dropbox

My editor and art director are running into issues with collaborating through indesign and incopy via dropbox. This hasn't been an issue before and we are trying to figure out what the source of the problem is. Our art director will save her indesign file to dropbox which is then opened by our editor to incopy but is receiving this error currently: 

Cannot open "InCopyTest_1.4.23.indd"

We need to be able to work off dropbox as our server in order to manage live edits. Any idea what the issue could be?