Question : A simple secuiry question

I created a group and added members to the group.

I have mapped the group to the desired database and the role is set to 'Public'.

When I run the SSRS report it says 'The SELECT permission was denied on the object 'D_Codes', database 'Month 2 2010 Actual', schema 'dbo'.

I am a junior when it comes to security. What do I need to do to sort this out?

Thanks

Answer : A simple secuiry question

You must grant SELECt permission for this group.
In same place where you select public you must check also db_datareader.