Access is denied: 'Microsoft.Samples.ReportingServices.CustomSecur

I am installing Reporting Services on a Veritas cluster environment on a
named Instance of SQL Server. The installation seems to go OK, but
afterwards when I try to call up the ReportManager I get this error:
Access is denied: 'Microsoft.Samples.ReportingServices.CustomSecurity'
I'm using a Domain Account with administrator privlidges, so I'm not sure
what to do next? Can anyone help?
thanksHere, I think, your report manager is somehow refering to custom
security extension which is configured in configuration files. Please
check if ur RM is pointing to proper server.
Thanks,
Mahesh