Its not just Castle that has disappeared from the boxsets, there are a shed load of others. On WEdnesday, on the V+Box HD, in the ABC section of the boxsets, there was at least 4 pages of boxsets available. Right now there are two.
I have spent the last 24 hours on the phone to VM, to get this checked out, and this morning, I have finally managed to get through to someone in 2nd Line support who is looking at the issue. He is curious now as to whether this was a local event or nationwide, but judging from this thread, its nationwide!