Microsoft report designer - "The entity with name=" " was not found in metadataCache" for custom entities

Hi all, 

I'm creating a report using fetch XML for CRM 2011. 

I used fetch query against the out-of the box entites and it worked fine. How ever, for custom entities, I get the following error.

" Could not create a list of fields for the query . verify that you can connect to the datasource and that the syntax is correct.

The entity "EntityName  " cannot be found. 

The entity with name ="EntityName" was not found in the metadataCache."