Yazid,
Its been 2 years so I will do my best. Alfresco my have changed this but if they are still using jBPM3.2 I suspect that it is the same.
The integration of jBPM within Alfresco has had the jBPM users/roles/groups removed.
The users/roles/groups that are used within Alfresco are Alfresco defined users/roles/groups. i.e. not jBPM users and groups. This breaks the jBPM console as nothing is ever loaded into the users table. If I remember correctly Alfresco actually removed the tables from their jBPM database. You would have to verify that. My experience was OK with what Alfresco had done. It worked but it was not what I expected as a jBPM user. I would not have integrated it in this manner. Way too difficult to maintain, upgrade and understand.
JIm