CDR files won't preview in dropbox :(

So for years, we have saved CDR files in dropbox and shared them between our team with no problem.  We were able to pull folders up and see the thumbnail of the image.  Now, I open a folder and I can't see any preview.  It just says it won't support cdr files or that they are likely too big.... if that is the case, how was I able to preview for so many years with no problem?  What gives?  I am soooo frustrated and my work is backing up because of this issue.  Help!

Jess