Prompted report caches can only be created or used for a project if the 'Enable caching for prompted reports and documents' check box is selected. Generally this option is checked by default.
Users can follow the below steps to enable caching for prompted reports:

Note: After executing a prompted report, a cache file will be generated. However if the report is saved, the report version will change, resulting in the cache file becoming invalidated. In order to maintain a valid cache for prompted reports, users should exit out of the report without saving it. This applies to saving the report as STATIC or PROMPTED.
This issue has been logged as Scopus ID: 397834 and KB ID: 17632