Test generation failure - does not exist

[ejaenv]

I get this error when I try to generate in eclipse a Testcase (I select class and then I choose CodePro tools > generate test case)

!MESSAGE Failed during test case generation

!STACK 1

org.eclipse.core.runtime.CoreException:  does not exist

at com.instantiations.assist.eclipse.junit.ui.util.NewTestCaseGenerator.configureProject(NewTestCaseGenerator.java:653)

at com.instantiations.assist.eclipse.junit.ui.util.NewTestCaseGenerator.createTestProjects(NewTestCaseGenerator.java:482)

at com.instantiations.assist.eclipse.junit.ui.util.NewTestCaseGenerator.generateAllTestCases(NewTestCaseGenerator.java:318)

at com.instantiations.assist.eclipse.junit.ui.util.NewTestCaseGenerator.generateTestCases(NewTestCaseGenerator.java:271)

at com.instantiations.assist.eclipse.junit.generation.core.TestGenerationService$TestGenerationJob.generateTests(TestGenerationService.java:214)

at com.instantiations.assist.eclipse.junit.generation.core.TestGenerationService$TestGenerationJob.runInWorkspace(TestGenerationService.java:190)

at org.eclipse.core.internal.resources.InternalWorkspaceJob.run(InternalWorkspaceJob.java:38)

at org.eclipse.core.internal.jobs.Worker.run(Worker.java:54)

!SUBENTRY 1 com.instantiations.assist.eclipse.junit 4 0 2012-03-24 22:50:00.862

!MESSAGE  does not exist

what is going wrong?