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.