Hi folks, though this thread is closed to further replies I just though I'd leave a note here to let you know that I'm looking in to this. I'm rebuilding the user cache and will check to ensure that this has been automatically refreshing itself periodically (which it should). Failing that, I'll get in touch with our database guru to ensure everything is running as it should be.
In the mean time, I do apologise for the inconvenience and hope this can be resolved ASAP.