linking workbooks:couple days

Hi. I am creating a report in which I have several workbooks linked into one. Most of my links work fine, but some of them only seem to work when the source workbook is open. Instead I get #n/a errors or 0.
This issue seems to be limited to only two of the workbooks, however not all the links from those workbooks aren't working. This only started recently,up until the a couple days ago I did not have this problem. I have made no changes to these links that would explain the change. I understand this happens when you have links to other files inside formulas, but do you have any ideas about how to fix this?

Thanks,
Allison

Anyone have any suggestions concerning the above issue?