Errors when installing the sampel adventureworks database for SQL Server 2012 RC0

I installed SQL Server 2012 RC0 today. Then I tried to install the sample database, using the following code:

CREATE DATABASE AdventureWorks2008R2
 ON (FILENAME = 'C:\AdventureWorks2008R2_Data.mdf')
 FOR ATTACH_REBUILD_LOG ;

I got the access deny error. Then I changed it to the D drive. It worked. Someone says that this is because of the compressed volume issue. But both C and D are not compressed. Why???