Immigration Clearance for Canadian Citizenship grant

[Rabi]

Hi all,
Appreciated if someone can share thoughts or experience.
I submitted my Citizendhip application in sometime Jun 2009. File is in Mississauga office since May 2010. I have not got any further communication or response for test. I have beenn informed that Mississauga office is waiting for "immigration clearance". Can some one advise what is this means and what checks are required and what might be approximate timelines in these kind of cases.