Please follow the below answer of this community thread
Error: "No PDF report returned from Crystal Web Service" | IFS Community

Follow the below steps to resolve the issue with required backups.

1. Take the initpub backup.
2. Uninstall the crystal services.
3. Re install crystal service from new zip in IFS instance folder (install CWS from IFS Home)
4. Restart the IIS.
5. Retry generating the PDF report

Hi @tariq ,

Still if you have any issues, please enable the logs;

• The CR_Web_Log.exe which can be found in the Web Service instance folder could be used to configure logs for that particular instance.
• Once the logs are configured, you should make sure that the Windows security group IIS_IUSR has read, write and modify access the logging folder that you specify under "Log File Location".

Then check on

→ Enable logging for IFSCRWebsetup

→ Log Level : High

Give a try to run a report and if you get the issue still, check the logs in the Log File location. 
Based on that information, you’ll be able to narrow down the problem.