Cron has been running for more than an hour and is most likely stuck.

Hi guys,

I've searched the issue queue but can't seem to find a notice of this.

My cron has stopped sending and gives me the message :- "Cron has been running for more than an hour and is most likely stuck.". There is no message in the PHP error log about anything untoward, it simply doesn't compelte the cron and so no subscriptions are sent out.

I implemented the cron tracking script and it appears to be falling over on subscriptions_mail_cron. :-

cron 09/01/2011 - 07:19 subscriptions_mail_cron invoked. admin
cron 09/01/2011 - 07:19 statistics_cron ran for 0.000255 seconds. admin
cron 09/01/2011 - 07:19 statistics_cron invoked. admin
cron 09/01/2011 - 07:19 signwriter_cron ran for 0.000688 seconds. admin
cron 09/01/2011 - 07:19 signwriter_cron invoked. admin
cron 09/01/2011 - 07:19 search_cron ran for 0.001993 seconds. admin
cron 09/01/2011 - 07:19 search_cron invoked. admin
cron 09/01/2011 - 07:19 node_cron ran for 0.000340 seconds. admin
cron 09/01/2011 - 07:19 node_cron invoked. admin
cron 09/01/2011 - 07:19 mollom_cron ran for 0.000234 seconds. admin
cron 09/01/2011 - 07:19 mollom_cron invoked. admin
cron 09/01/2011 - 07:19 logintoboggan_cron ran for 0.000032 seconds. admin
cron 09/01/2011 - 07:19 logintoboggan_cron invoked. admin
cron 09/01/2011 - 07:19 googleanalytics_cron ran for 0.000035 seconds. admin
cron 09/01/2011 - 07:19 googleanalytics_cron invoked. admin
cron 09/01/2011 - 07:19 filter_cron ran for 0.000362 seconds. admin
cron 09/01/2011 - 07:19 filter_cron invoked. admin
cron 09/01/2011 - 07:19 fb_devel_cron ran for 0.000563 seconds. admin
cron 09/01/2011 - 07:19 fb_devel_cron invoked. admin
cron 09/01/2011 - 07:19 dblog_cron ran for 0.001112 seconds. admin
cron 09/01/2011 - 07:19 dblog_cron invoked. admin
cron 09/01/2011 - 07:19 date_timezone_cron ran for 0.006702 seconds. admin
cron 09/01/2011 - 07:19 date_timezone_cron invoked. admin
cron 09/01/2011 - 07:19 Cron invoked admin
warning cron 09/01/2011 - 07:18 Attempting to re-run cron while it is already running. admin
cron 09/01/2011 - 07:18 Cron invoked admin

It is not a large site, in fact, it's new so less than 10 people are registered for subscriptions. Is there any further debugging I can invoke to find out what the issue is?

Drupal 6.1
Subscriptions 6.x-1.x