I'm getting the same error. I'm using the most recent version of Knowage Studio CE 6.1.0 for Windows 64 Bit on a Windows 7 workstation with Java 1.8_101. This is a BIRT Report.
I should note that when it is deployed to the Knowage 6.1 CE server on a Linux host, the report will run correctly.
I also noticed that you cannot perform any updates on the Studio itself. I suppose there's a reason for that, given that you are using a very old version of Eclipse RCP (Luna), but it would be nice to be able to fix this through such a mechanism.