Encountered this issue a few times when deploying CRM over multiple servers then trying to run reports/custom reports through the standard report builder , solution:
– Open IIS on the server CRM 2011 is installed on
– Expand the server name
– Click ‘Application Pools’
– Look for ‘CRMAppPool’ and the account it’s running on (e.g. DOMAINCRMApp) and note down the account name.
– Log into your CRM SSRS server
– Open CMD Prompt as administrator and run the following command: ‘setspn -a http/SERVERNAME DOMAINIISACCOUNT’ (IIS Account being the application pool account you noted down from IIS)
Once you’ve done this, you should be able to run reports without getting the Target SPN error in the SSRS logs.