A few weeks ago, I created a document with links to several Dropbox documents, which were working fine for me and the other users I sent it to. I was just emailed by them, however, who said that links no longer work for them. I opened my version of the document, click on them and they work fine, taking me to the Dropbox page where the document is. I re-sent the documents to them but they say still they cannot access them. Any suggestions on what may have happened? I did not change the location of the folder with the files and I had not set expiry date for the links.