I found a strange error about a missing command handler in our application when installing a newer release for our customer:
org.eclipse.core.commands.NotHandledException: There is no handler to execute for command ...
I checked the plugins and everything else and found that the handler is actually there, activated, visible, etc. Now the strange thing: the error can be solved by deleting the user's workspace folders (in addition to the runtime folders that happens when starting with -clean). But I cannot find anything related to the commands or handlers. There is a lot of data about column orders, windows sizes and so on, so I can't just wipe these data away for production.
What cached data may cause this effect?
We're stuck to RCP 3.4 right now.
I found that the issue can be solved by removing the file .metadata/.plugins/org.eclipse.core.runtime/.settings/org.eclipse.ui.workbench.prefs from the workspace.
The file contains perspective IDs as keys, and a XML structure as values. Removing a single line of this file that refers to a perspective solves the problem for that perspective.
I noticed that the perspectives were referenced by their short name (without the package) before, and with their fully qualified name after the new release. So there must be some side-effect when using the old prefs causing the handlers do not work anymore.