This problem has been annoying me for a while, especially when you design reports through Crystal Reports. I have tried many different ways which searched from Internet, but none of them work for my case, maybe it should depend on your reports situation to use different methods to fix this error message. Please see the following steps for your reference:
1. Go to File, and tick off Save Data with Report.
2. Rerun the report.
3. Tick Save Data with Report.
4. Save it!