Android: adt was unable to instantiate class com.android.ide.eclipse.adt.internal.editors.common.CommonXmlEditor -

I see this problem when I try to open any XML file in Eclipse:

The plug-in was unable to administer the "com.android.ide.eclipse.adt" class "com.android.edroid.ede.eillipple.edit.in.editers.com comonaxml editor".

How do I solve this problem?