There can be many reasons for this.
1. Make sure the mobile's connection is good (see network icon at top of screen). You (or the human resource) can also try to open the mobile's browser; if you can't open a web page, there is a connection problem. Check your connection information.
2. Make sure the human resource supposed to receive the task is linked to a user, and the right user.
3. The selected user must have a mobile configuration to receive tasks. In addition, make sure that you are waiting at least as long as the synchronization time selected in the "Mobile configuration" associated with the user.
4. Make sure the task is of a type for which the "Mobile dispatchable" box is checked.
5. Make sure the content of the "Received" column in the task list contains a date. Maybe the user is just having trouble locating the task in his or her list.