Notifications queue does not create privatemessages - email notifications

Hi all,
My setup is

drupal 6.14
notifications 6x-2.2
messaging 6x-2.2
Privatemsg 6.x-1.0
PHP ver 5.2.11 on Centos 5

----------------------------
I have problem with the notifications and i don't know what is going wrong. The problem is the following.
I want to notify my site users for new content creation for several content types (content type subscriptions).
Users subscribed to a content type with notification interval 0 and digest none takes notifications (pm & email notifications) only if the Immediate sending is checked on /admin/messaging/notifications . That is very heavy because the total number of subscriptions must be processed on save - update of the content.
I tried to change to all users subscriptions the send interval to hourly so the notifications will be processed by cron later.
On a content creation - update the notifications_queue table, filled with the right number of rows according the number of subscriptions.
After an hour the notifications_queue has all rows processed ( cron field = 0 and send field has a timestamp ) but none of my users has a new pm and as I can see on my smtp server logs , none email send.

So the only working condition is checking the immediate sending on notifications settings, and all the subscribers must set their prefered send interval to 0 ..

Any idea????

PS. I tried to change the process limits for cron both on messaging and notifications settings with no result, but i am not so sure if my settings was recomended.