eclipse could not find default drools runtime

Problem Statement: eclipse could not find default drools runtime

Solution: 
Edit .project file in your project directory, from the .project file delete following:

<buildCommand>
     <name>org.drools.eclipse.droolsbuilder</name>
     <arguments>
     </arguments>
</buildCommand>

then re-import your project into workspace. Delete it, without deleting from file system, and then import it as existing project.