Cronjob fails to run with Subscription enabled

Hello, all.

I have an issue with my Drupal 5.10 website and would appreciate if someone could help me and give me some insight about what I could do to solve it. The situation is the following:

The website is installed in Dreamhost and it is not the busiest place on Earth. Still, it is updated quite often, and most of my users have set up to receive notices on their e-mails about new content. I use Subscription in order to do this and I know it is working and running, and that my CronJob is configured correctly, because the first time I run it, after cleaning the subscription_queue table and following the directions that I found here:

http://www.mojahmedia.net/drupal-cron-run-failed-cron-busy-probably-stuc...

It works perfectly. Meaning that I do receive the first e-mails that are sent after a "new instalation". Still, after a couple of times that it has run, for some reason I start getting the message that Cron has failed to run. And when I check while, it says "Cron is already running". And then I have to go through all the steps again:

- Disabling Subscription module
- Cleaning subscriptions_queue table
- Deleting cron variables from the DB:

DELETE FROM `variable` WHERE name = 'cron_semaphore';
DELETE FROM `variable` WHERE name = 'cron_last';

- Enabling Subscriptions again
- Running Cron.

And then it works. For the first couple of times. And then, DUNG. Stops working again and I have to start it over from the beginning.

The current configuration that I have is the following:

- Cron runs every 20 minutes
- Subscription should send up to 50 e-mails every time Cron runs (it is not much, in my other server it could send up to 300 without problem)
- Index 10 pages at a time, in the search module

Versions of Subscription: 5.x-2.3

The site is this one: http://www.redehumanizasus.net/

Thank you so much for your help.

Best regards,

danimatielo