We've had an annoying issue with the Notes client, since release 8 and the introduction of the Eclipse framework; Every so often the "data\workspace" folder goes corrupt. This is the Eclipse framework workspace and should not be confused with the Workspace in the client.
A symptom of a corrupt workspace, is that the Notes client simply hangs at the Splash screen, after entering your password. Killing the "IBM Notes" process in Task Manager and then deleting/renaming the "data\workspace" folder always resolves the issue, as the workspace is automatically re-created.
Can you perhaps add an integrity check and self-repair of the Eclipse framework "data\workspace" folder on client startup?