Have you checked the error log located in /var/hda/web-apps/ajaxplorer/logs? Also recommend you check the AjaXplore web site or bug tracker to see if this might be identified as a problem.
Check the ownership and permissions of the files in question. They should be owned by your first admin user and set to 775 at a minumum.
If you want to access files outside your network, OpenVPN ALS is a better choice in my opinion.
http://www.amahi.org/apps/openvpn-als
If it's just inside your network, can you describe your requirements? Many use the client file manager to view files vs a web app.