I am using Report Builder 2.0 Version 10.0.2746.0 connecting to a model that is on 

Microsoft SQL Server 2008 (SP1) - 10.0.2734.0 (X64)   Sep 11 2009 14:30:58   Copyright (c) 1988-2008 Microsoft Corporation  Developer Edition (64-bit) on Windows NT 6.0 <X64> (Build 6002: Service Pack 2) 

I connect to the model and design a simple report that returns 3 fields from the same table.  No parameters added to the report.  Just a basic SELECT field1, field2, field3 FROM table1 

When I run the report, I get "Some parameters or credentials have not been specified".  
I click the refresh button in the report builder ribbon and data returns.  
I click refresh again...."Some parameters or credentials have not been specified".  
Click again: "Some parameters or credentials have not been specified".  
Click again: data returns.
Click again: data returns.
Click again: "Some parameters or credentials have not been specified"

The report server is NOT in a cluster.

If Some parameters or credentials have not been specified, shouldn't I be getting the error all the time?