We're running CiviCRM 4.7.13 on Drupal 7.51 on a shared server.

I am the administrator for our site and AFAICT, I have admin privileges for everything.  However, whenever anyone, myself included, opens a report (eg Membership Detail report), we can view the results on screen, page through them etc., but we can't print the report, print to PDF or export as CSV, all we get in each case is the 403 "Forbidden" error.

My main problem trying to work out the cause of this problem is finding some sort of error message.  Thanks to http://civicrm.stackexchange.com/questions/15915/how-do-i-find-error-log-to-see-what-is-causing-the-error and pages linked from that question I've been able to locate our PHP log file and our CiviCRM log file but neither shows any entries that are obviously related to this problem.

I believe this is a symptom of some broader issues we have with the Organic Groups module on our site so I am mainly looking for tips on increasing the usefulness of existing logs (or any other logs I should be looking for).  Other questions on those topics haven't helped me so far.

TIA,