Access privileges to Word files that I created and stored in Dropbox are denied.

I have been using Dropbox for years with no problem until now. I recently acquired a new iMac desktop, but when I opened Dropbox on it I discovered that it will no longer let me edit Word (.docx) files that I created and stored on Dropbox. I get a message that additional permissions are needed, and then that the Word document cannot open as user does not have access privileges to files that I created. I can view the file, but I cannot edit it. However, if I go back to my laptop I can open, view, and edit files I created.