I'm running Eclipse Neon (tried with Mars too) and Liferay 6.2
I try to run the service builder but:
Yes, I've cleaned everything before. In fact, I created a brand new project, in an Eclipse with only jre7 installed, pointing all to jre7 (compiler, facets...)
Eclipse is running over jre8, but can't run on jre7 because some of the plugins requires jre8. Anyway, some days ago it do worked in this Eclipse, so it's not the problem.
Service Builder might pull code from more than your Eclipse project setup - e.g. from the running Liferay installation that the plugin sdk points to.
I've not heard of a com.aspr.seu package in Liferay - is that your own, or unknown to you as well?
If service builder ran in the past (e.g. with Java 8), it created a yourprojectname-service.jar - that might be one that is pulled into the build process and that you might not have cleaned yet. You definitely have a class that was built with Java 8 on the classpath, you'll just need to find it. It might help to know that servicebuilder is executed through an Ant task outside of Eclipse, thus it might not be enough to search through all of the files that Eclipse has configured on its classpath, but rather on what's configured for the Plugins-SDK