By default Crystal Reports 2011 and 2013 install Java drivers in the following location:
C:\Program Files (x86)\Business Objects\Common\4.0\java\lib\.
The Report Viewer does not install Java libraries. But, it will look for them in the following location:
C:\Program Files (x86)\SAP Business Objects\SAP BusinessObjects Enterprise XI 4.0\java\lib\.
So, copying your Java drivers from a working install of Crystal Reports to a client system with The Report Viewer installed, may be required to connect using a native Java driver.
Once you copy the files over, you will likely need to update the CRConfig.xml file at the new location.
Please review this documentation: