wp-cron processes taking too long

Hi there,

My host has been emailing me saying that wp-cron.php is taking too long and overloading the server.

It regularly takes 600+ seconds to run the script.
I had a look at error_log and i’m getting bunch of errors that vaguely match the emails my host is getting warning him about the wp-cron.php taking too long.
Here is what the errors look like:

[31-Mar-2011 16:53:45] PHP Warning:  preg_match() expects parameter 2 to be string, array given in /home/mefree/public_html/wp/wp-includes/comment.php on line 1615
[31-Mar-2011 17:40:52] PHP Warning:  preg_match() expects parameter 2 to be string, array given in /home/mefree/public_html/wp/wp-includes/comment.php on line 1615
[31-Mar-2011 20:32:24] PHP Warning:  preg_match() expects parameter 2 to be string, array given in /home/mefree/public_html/wp/wp-includes/comment.php on line 1615
[31-Mar-2011 20:32:37] PHP Warning:  preg_match() expects parameter 2 to be string, array given in /home/mefree/public_html/wp/wp-includes/comment.php on line 1615
[31-Mar-2011 20:33:19] PHP Warning:  preg_match() expects parameter 2 to be string, array given in /home/mefree/public_html/wp/wp-includes/comment.php on line 1615
[01-Apr-2011 13:55:15] PHP Warning:  preg_match() expects parameter 2 to be string, array given in /home/mefree/public_html/wp/wp-includes/comment.php on line 1615
[01-Apr-2011 13:55:21] PHP Warning:  preg_match() expects parameter 2 to be string, array given in /home/mefree/public_html/wp/wp-includes/comment.php on line 1615
[01-Apr-2011 14:00:11] PHP Warning:  preg_match() expects parameter 2 to be string, array given in /home/mefree/public_html/wp/wp-includes/comment.php on line 1615

I’m running wordpress 3.1 with the standard twentyten theme. I’ve basically tried deactivating all my plugins but that hasn’t worked.

Would love some help; Our website is for a non-profit organisation and our host kindly donates space and bandwidth. I’d hate to be the cause of problems for his other clients.