Description:
The full stack for the second message is found below and will be found by clicking on "Details" or by running studio -debug .

ENTRY org.eclipse.equinox.registry 4 1 2011-05-23 15:14:13.163
!MESSAGE Unable to create view ID com.tibco.cep.studio.projectexplorer.view: Plug-in com.tibco.cep.studio.ui.navigator was unable to load class com.tibco.cep.studio.ui.navigator.view.ProjectExplorer.
!STACK 0
org.eclipse.core.runtime.internal.adaptor.EclipseLazyStarter$TerminatingClassNotFoundException: An error occurred while automatically activating bundle com.tibco.cep.studio.core (27).
    at org.eclipse.core.runtime.internal.adaptor.EclipseLazyStarter.postFindLocalClass(EclipseLazyStarter.java:125)
    at org.eclipse.osgi.baseadaptor.loader.ClasspathManager.findLocalClass(ClasspathManager.java:427)
    at org.eclipse.osgi.internal.baseadaptor.DefaultClassLoader.findLocalClass(DefaultClassLoader.java:193)
    at org.eclipse.osgi.framework.internal.core.BundleLoader.findLocalClass(BundleLoader.java:370)
    at org.eclipse.osgi.framework.internal.core.BundleLoader.findClassInternal(BundleLoader.java:446)
    at org.eclipse.osgi.framework.internal.core.BundleLoader.findClass(BundleLoader.java:399)
    at org.eclipse.osgi.framework.internal.core.BundleLoader.findClass(BundleLoader.java:387)
    at org.eclipse.osgi.internal.baseadaptor.DefaultClassLoader.loadClass(DefaultClassLoader.java:87)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:248)

Symptoms:
Either error message can be taken as a symptom of this problem.
Cause:
The Workspace is corrupt and the cache stored there is stale or there is a malformed XML in .beproject. If the .beproject is bad, you will see the following on the stack trace.

Caused by: org.eclipse.emf.ecore.resource.impl.ResourceSetImpl$1DiagnosticWrappedException: org.xml.sax.SAXParseException: The content of elements must consist of well-formed character data or markup.
        at org.eclipse.emf.ecore.resource.impl.ResourceSetImpl.handleDemandLoadException(ResourceSetImpl.java:315)
        at org.eclipse.emf.ecore.resource.impl.ResourceSetImpl.demandLoadHelper(ResourceSetImpl.java:274)
        at org.eclipse.emf.ecore.resource.impl.ResourceSetImpl.getResource(ResourceSetImpl.java:397)
        at com.tibco.cep.studio.core.util.CommonUtil.loadEObject(Unknown Source)
        at com.tibco.cep.studio.core.util.CommonUtil.loadEObject(Unknown Source)
        at com.tibco.cep.studio.core.configuration.manager.StudioProjectConfigurationManager.createConfigurationFromProject(Unknown Source)
        at com.tibco.cep.studio.core.configuration.manager.StudioProjectConfigurationManager.load(Unknown Source)
        at com.tibco.cep.studio.core.configuration.manager.StudioProjectConfigurationManager.getInstance(Unknown Source)

StudioProjectConfigurationManager is the key element when you have bad XML in the .beproject.

TIBCO BusinessEvents (BE) 4.0.1 Studio fails to start and throws the error, "Product com.tibco.cep.studio.application.product could not be found. Or was unable to load the class com.tibco.cep.studio.ui.navigator.view.ProjectExplorer."

Resolution:
=========
Start Studio and create a new Workspace and import the project into the new Workspace.

Or

Edit your .beproject Project Directory to removed the incorrect XML.