This could depend on the version of java pointed by WebRatio 7 on startup. In fact WebRatio 7 is compatible only with java 7 (and not with higher versions).
Please refer to these topics and answers:
Anyway you can install different java versions on your machine and set the correct path in the WebRatio.ini file (e.g. java 7 path for WebRatio 7 and java 8 path for WebRatio 8).
For more details on the requirements, refer to the Release Notes: