When I try to export my Call List (containing 400+ calls) by clicking on the Export link at the top left of the Call list I get the following error:

Fatal error: export(): Failed opening required '' (include_path='.:/home/oldwww/php//lib/php') in /home/www/htdocs/SugarSuite-Full-3.5.1a/export.php on line 164

(ignore the version number in that error message - it is simply a result of an unfortunately-named folder on the server!)

Exports from all other modules work fine, and exports of Meetings, Tasks, and Notes in the Activities module also work fine. Any ideas?

Sugar Version: 4.2.0d
Sugar Edition: Sugar Open Source
Category: Activities
Operating System: Linux (unsure of version)
PHP Version: Unsure
Database: MySQL (unsure of version)
Web Server: Apache (unsure of version)