While testing MDLQA-1121
I created a community search block, clicked "Search" and then searched with all the default field values
The error appears:
An error occured when retrieving the course listing from the selected hub, please try again later. (Access control exception)

Error log is:

[Wed Jun 22 10:06:42 2011] [error] [client 203.59.94.230] PHP Warning: Cannot modify header information - headers already sent by (output started at /html/question/format/qti_two/format.php:565) in /html/lib/filelib.php on line 1803, referer: http://qa.moodle.net/question/export.php
[Wed Jun 22 10:06:42 2011] [error] [client 203.59.94.230] PHP Stack trace:, referer: http://qa.moodle.net/question/export.php
[Wed Jun 22 10:06:42 2011] [error] [client 203.59.94.230] PHP 1.

() /html/pluginfile.php:0, referer: http://qa.moodle.net/question/export.php
[Wed Jun 22 10:06:42 2011] [error] [client 203.59.94.230] PHP 2. question_pluginfile() /html/pluginfile.php:658, referer: http://qa.moodle.net/question/export.php
[Wed Jun 22 10:06:42 2011] [error] [client 203.59.94.230] PHP 3. send_file() /html/lib/questionlib.php:1767, referer: http://qa.moodle.net/question/export.php
[Wed Jun 22 10:06:42 2011] [error] [client 203.59.94.230] PHP 4. header() /html/lib/filelib.php:1803, referer: http://qa.moodle.net/question/export.php
[Wed Jun 22 10:06:42 2011] [error] [client 203.59.94.230] Default exception handler: Can not serve file - server configuration problem. Debug: Headers already sent, can not serve file.\n* line 1555 of /lib/filelib.php: file_serving_exception thrown\n* line 1807 of /lib/filelib.php: call to prepare_file_content_sending()\n* line 1767 of /lib/questionlib.php: call to send_file()\n* line 658 of /pluginfile.php: call to question_pluginfile()\n, referer: http://qa.moodle.net/question/export.php