On the grader report, after turning editing on and clicking in any grade field after 1 character is typed the page hangs for a while (around 15 seconds) when using Chrome and Firefox. Internet Explorer does not have this issue. The gradebook where this happens uses categories to organise the grade items. There are 98 students on the course and around 35 grade items.

With debugging turned on I get the following errors when the page loads:

faultCode0faultStringNotice:Undefined property: stdClass::$httpsthemewww in /data/apache/htdocs/moodle/theme/ucl/renderers.php on line 144faultCode0faultStringNotice:Undefined property: stdClass::$httpsthemewww in /data/apache/htdocs/moodle/theme/ucl/renderers.php on line 162

faultCode0faultStringNotice:unserialize(): Error at offset 249 of 255 bytes in /data/apache/htdocs/moodle/grade/report/grader/lib.php on line 112
Separate groups
faultCode0faultStringWarning:in_array() expects parameter 2 to be array, null given in /data/apache/htdocs/moodle/grade/report/grader/lib.php on line 1502faultCode0faultStringWarning:in_array() expects parameter 2 to be array, null given in /data/apache/htdocs/moodle/grade/report/grader/lib.php on line 1506faultCode0faultStringWarning:in_array() expects parameter 2 to be array, null given in /data/apache/htdocs/moodle/grade/report/grader/lib.php on line 1502faultCode0faultStringWarning:in_array() expects parameter 2 to be array, null given in /data/apache/htdocs/moodle/grade/report/grader/lib.php on line 1506

On loading the page I also get 2 javascript errors in the console:
GET https://moodle2-uat.ucl.ac.uk/grade/report/grader/%3C?xml%20version= 404 (Not Found)
index.php:5223GET https://moodle2-uat.ucl.ac.uk/grade/report/grader/%3C?xml%20version= 404 (Not Found)

Similar issues have also been reported here:
http://moodle.org/mod/forum/discuss.php?d=188756
http://moodle.org/mod/forum/discuss.php?d=142129