While messing around with authentication options I receieved:
Server Error in '/Reports' Application.
Object reference not set to an instance of an object.
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.
Exception Details: System.NullReferenceException: Object reference not set to an instance of an object.
An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below.
[NullReferenceException: Object reference not set to an instance of an object.]
Microsoft.ReportingServices.UI.GlobalApp.Application_AuthenticateRequest(Object sender, EventArgs e) +73
System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +176
Version Information: Microsoft .NET Framework Version:2.0.50727.1433; ASP.NET Version:2.0.50727.1433
To solve this: Change the asp.net configuration to be windows authentication rather than none on the reportmanager virtual directory (asp.net tab - edit configuration and change auth there).
This was my own fault but in case anyone else does the same thing while playing around with authentication options in reporting services this may help : )