Hi Ivy,
When you install SQL Server 2008R2, did you login as ivykwok? if so, I think you can try "Add Current User" button to add that user, so that you can use that user on Analysis Service.
If I mis-understood your issue, maybe you can try to move this post to SQL Server and Business Intelligent section in this forum. I think you can get more help about SQL Server easiler
Please find the SQL Server and Business Intelligent section URL below
http://social.microsoft.com/Forums/zh-hk/sqlserverzhcht/threads
Good Luck
Chi