FYI: Fix for Eclipse error "The following problem occurred, xyz.jar was referenced by the classpath, does not exist"

[Legaia]

I was trying to get an auto generated serial version UID from a new
class, but it kept giving me this error. What was crazy was that the
jars DO exist.

I just wanted to post the solution. Maybe the next time I google I'll
find my own message again - ha!

So anyways, try blowing away your Servers project and recreating. I
also deleted my Eclipse project and did a fresh checkout from SVN for
good measure. Very irritating.

It was a dynamic web project, so I figure the problem is coming from
Web Tools Platform. I've got this message in my log over and over
again, so I suspect this is the root cause under the covers:

!ENTRY org.eclipse.wst.validation 4 0 2008-10-20 09:55:05.783
!MESSAGE
*** ERROR ***: Mon Oct 20 09:55:05 EDT 2008
org.eclipse.core.internal.resources.ResourceException: Marker id
638350 not found.
at
org.eclipse.core.internal.resources.Marker.checkInfo(Marker.java:56)
at
org.eclipse.core.internal.resources.Marker.getAttribute(Marker.java:
97)
at
org.eclipse.wst.validation.internal.TaskListUtility.getValidationTasks(TaskListUtility.java:
331)
at
org.eclipse.wst.validation.internal.TaskListUtility.getValidationTasks(TaskListUtility.java:
390)
at
org.eclipse.wst.validation.internal.TaskListUtility.getValidationTasks(TaskListUtility.java:
443)
at
org.eclipse.wst.validation.internal.TaskListUtility.removeTaskSubset(TaskListUtility.java:
543)
at
org.eclipse.wst.validation.internal.TaskListUtility.removeAllTasks(TaskListUtility.java:
523)
at
org.eclipse.wst.validation.internal.TaskListUtility.removeAllTasks(TaskListUtility.java:
519)
at
org.eclipse.wst.validation.internal.operations.WorkbenchReporter.removeAllMessages(WorkbenchReporter.java:
207)
at
org.eclipse.wst.validation.internal.operations.WorkbenchReporter.removeAllMessages(WorkbenchReporter.java:
672)
at
org.eclipse.jst.j2ee.model.internal.validation.WarValidator.validateInJob(WarValidator.java:
319)
at
org.eclipse.jst.j2ee.internal.web.validation.UIWarValidator.validateInJob(UIWarValidator.java:
111)
at
org.eclipse.wst.validation.internal.operations.ValidatorJob.run(ValidatorJob.java:
75)
at org.eclipse.core.internal.jobs.Worker.run(Worker.java:55)