Private Task does not work SAP CRM

Hi Experts!

I'm facing a problem in SAP CRM 7.0  When I try to create a private task the checkbox field "Private" is empty and is not changeable

I found the next sap note:

1631251  - Checkbox 'Private' is not changeable in activities and tasks

I followed the customizing steps but I didn't obtain that the task working as I need.

Anybody knows what is the problem?

Thank you for your help.

Maria.