Ads in my installation AdsManagercan not expired (deleted)

I test AdsManager v. 3.0.2 FREE on Joomla 2.5.27:
address of test: http://www.joomlapolis.cz/test/silvtest/inzeraty

I have set in configuration:
type cron: onuserrequest
Allow expiration ads: Yes
Time to Expiration: 45 days
Ads after expiration: delete

There are ads older than 45 days, but they can not delete.
What can be wrong?
When is set ty cron to: onuserrequest , how are the ads deleted?

Yes, I tried method WebCron, but it is not clear to me how this method works.
When I put in browser URL yourwebsite.com/index.php?option=com_adsmanager&task=cron, created a new table xxx_adsmanager_cron, but nothing else with expired ads.

Method Linux Task I can not set because I do not know how.

How method onuserrequest exactly works?
I understand that the expiration take place automatically, when I set method onuserrequest.

Hello,

I found the solution, it was pretty easy.
Expiration ads did not work, because there was a lack of user accounts Joomla.

All data in AdsManager v.3.0.2 I got through migration from the old version 2.5.0.
I performed the migration so that I imported to the new site database old tables AdsManager with data, and then I started to install AdsManager v. 3.0.2 on the new site.

All data was safely transferred to the new version.
But I did not transfer all user accounts from old Joomla, which have been linked to ads in AdsManager.
After migrating all user accounts, began expiration ads work.