I was attempting to install WebSphere Process Server v6.0.2.3 on the server installed with WebSphere Integration Developer. The install kept failing on me with an exception:

Caused by: com.ibm.ws.install.ni.framework.fileactions.NIFFileActionIOException:
The file java/jre/lib/charsets.jar could not be replaced.
at com.ibm.ws.install.ni.framework.fileactions.ReplaceFileActionPlugin.execute
(ReplaceFileActionPlugin.java:108)
at com.ibm.ws.install.ni.framework.fileactions.FileActionPlugin.executeFileAction
(FileActionPlugin.java:54)
at com.ibm.ws.install.ni.updi.component.was.ComponentFileActions.execute
(ComponentFileActions.java:95)
at com.ibm.ws.install.ni.updi.component.was.ComponentDeployAction.execute
(ComponentDeployAction.java:48)
at com.ibm.ws.install.ni.updi.component.was.UpdateComponent.execute
(UpdateComponent.java:93)
at com.ibm.ws.install.ni.framework.component.ComponentAction.executeComponentActions
(ComponentAction.java:215)
at com.ibm.ws.install.ni.framework.component.ComponentAction.executeComponentActions
(ComponentAction.java:75)
at com.ibm.ws.install.ni.framework.install.NIFPackageApplicationPlugin.performUpgrade
(NIFPackageApplicationPlugin.java:548)
... 16 more

I forgot to close my WebSphere Integration Developer. Once I closed it, the upgrade completed successfully.