Steps to recreate:

1) Create new JBossESB project in JBDS - use samples/quickstarts/helloworld
2) Attempt to export to .esb file

Attached log file shows the error raised - attached .tar file contains the project.

!ENTRY org.eclipse.wst.common.frameworks 4 0 2009-12-15 15:13:54.386
!MESSAGE Error exportinghello
!STACK 0
org.eclipse.core.commands.ExecutionException: Error exportinghello
at org.jboss.ide.eclipse.as.wtp.core.vcf.ModuleExportOperation.execute(ModuleExportOperation.java:117)
at org.eclipse.wst.common.frameworks.internal.datamodel.DataModelPausibleOperationImpl$1.run(DataModelPausibleOperationImpl.java:376)
at org.eclipse.core.internal.resources.Workspace.run(Workspace.java:1800)
at org.eclipse.wst.common.frameworks.internal.datamodel.DataModelPausibleOperationImpl.runOperation(DataModelPausibleOperationImpl.java:401)
at org.eclipse.wst.common.frameworks.internal.datamodel.DataModelPausibleOperationImpl.runOperation(DataModelPausibleOperationImpl.java:352)
at org.eclipse.wst.common.frameworks.internal.datamodel.DataModelPausibleOperationImpl.doExecute(DataModelPausibleOperationImpl.java:242)
at org.eclipse.wst.common.frameworks.internal.datamodel.DataModelPausibleOperationImpl.executeImpl(DataModelPausibleOperationImpl.java:214)
at org.eclipse.wst.common.frameworks.internal.datamodel.DataModelPausibleOperationImpl.cacheThreadAndContinue(DataModelPausibleOperationImpl.java:89)
at org.eclipse.wst.common.frameworks.internal.datamodel.DataModelPausibleOperationImpl.execute(DataModelPausibleOperationImpl.java:202)
at org.eclipse.wst.common.frameworks.internal.datamodel.ui.DataModelWizard$1$CatchThrowableRunnableWithProgress.run(DataModelWizard.java:218)
at org.eclipse.jface.operation.ModalContext$ModalContextThread.run(ModalContext.java:121)
Caused by: org.eclipse.jst.j2ee.commonarchivecore.internal.exception.SaveFailureException
at org.jboss.ide.eclipse.as.wtp.core.vcf.ModuleExportOperation.export(ModuleExportOperation.java:269)
at org.jboss.ide.eclipse.as.wtp.core.vcf.ModuleExportOperation.execute(ModuleExportOperation.java:114)
... 10 more