You can not use Context Variable values in the where clause of Report Views.
My use case:
I want a report for my sales representative person. He shall only see his own business partners. I did a report in the System client and used a "Report View". In this report view I can filter the report via a "SQL WHERE" clause. I thought I needed a string like "SalesRep_ID=@#AD_User_ID@" but it does not work. It looks like you can not use Context variables at this point.
(a42niem told me he is doing a similar report and it works for him. I looked into the code and I can't find the place where the @...@ is parsed. Perhaps he or me misunderstood that - just wanted to mention it here for the case I am wrong.)