You might not have permission to perform this operation, or the object <Objectname> might no longer exist in the database.
The object you want to work with may be listed, but you may not have SELECT permission to this object. Or, the object may no longer exist in the database.
For example, you may have created a table, but someone else may have modified your access rights and changed the owner of the table object to another. Because of these actions, you no longer have SELECT permission.
Refresh the list of objects to find out if this object still exists in the database. If this object still exists, then contact the owner of the object or the Database Administrator to get permission to this object.
For more information, see Ownership Chains.