In attempting to import course materials from another course into the present course, the "Import" button on the "Course administration" explorer goes through the following workflow:
1. "Find a course to import data from:" <chose a course> clicked "Continue"
2. "Backup settings" <chose "Include activities", "Include blocks", and "Include filters"> clicked "Next"
3. Server returned a list of all content components of the target course available for import. Chose all and clicked "Next"
4. Server returned a confirmation list with green checkmarks for components to import and red Xs for components not being imported. Top of page reports that we are at step 4: "Confirmation and review" task in the workflow. Got message "There are required fields in this form marked *" below the "Perform import" button (even though I could find no such fields--a search of the HTML code did not find any asterisk outside of HTML comment tags). Clicked "Perform import"
5. Received a HTTP 500 Internal Server Error.

Server error log reports:
[Thu Jun 14 16:20:17 2012] [error] [client xx.xx.xx.xx] File does not exist: <path to Moodle Document Root>/moodle/500.shtml, referer: http://moodle.<domainname>/backup/import.php

The same error is encountered when trying to backup a course.