Scenario: We currently have SQL Reporting Services 2008 R2 in a scale-out deployment on two servers. SSRS is configured in SharePoint integrated mode with our SharePoint 2010 servers (configured with NTLM authentication). We have numerous reports that work without issue.
Problem: On 3 of our reports, while running the report it prompts the user to login (even though they are already authenticated). Under any user accounts it prompts the user to login and fails to do so. The same reports work just fine when deployed to SSRS in Native Mode rather than SharePoint Mode.
Other reports use the same data connection without issue. And the users have contribute access to the folders that house the data connection, shared datasets, and the reports.