The error normally shows if the user account that is trying to access the report does not have the correct permissions.
Moving the report to a location that is accessible to everyone normally solves the issue.
Please see this thread on the SAP SCN: https://archive.sap.com/discussions/thread/2138029
The issue is the same as explained above but please note that the server component runs as under the local system account on the machine. This means that the local system account needs to have access to the Crystal or you can change the service to run under a different user account that has the correct permissions.
Edit: For server components and users this can be solved by making sure that the folder where the Crystal Reports are saved has set permissions for the user: "Everyone" to read. (Works on Cloudiax).