Namespace Geodatabase not found

[ShaningYu]

I am updating a WCF project.  I added the ESRI.ArcGIS.Geodatabase as the reference.  In the class, by referrring http://resources.esri.com/help/900/arcgisexplorer/sdk/doc/6b970ec8-9ab3-4837-969e-411bcf9789d3.htm, where
   Geodatabase gdb = new Geodatabase(@"C:\Data\Scotland.gdb");
I coded like that almost exact, such as:
   ESRI.ArcGIS.Geodatabase gdb = new ESRI.ArcGIS.Geodatabase();
But under the Geodatabase, I got the error warning:
ESRI.ArcGIS.Geodatabase' is a 'namespace' but is used like a 'type'
What's wrong I coded here?  Thanks.

[ShaningYu · Accepted solution]

Realized that in .net web project, can't work on Geodatabase directly.  Case closed.