PDFs stored on network share goes blank after 30 minutes

We are having issues with Adobe Reader XI on Windows 8. Most of our PDFs are stored in the network share. It opens just fine, but it goes blank after 30 minutes or so, as if it loses connection to the network share. We have to reopen the PDF and copy the file to another network share and it's resolved. Is there some type of setting in the security that terminates the connection after a given time? Thanks you in advance for your help.
