Does the exact configuration matter?
I'm not cleaning anything, it's a dummy operation...
Did you add (audio or other) files to the simdisk directory, or was this just the rockbox installation?
It fails with and without audio files - it seems that it manages to say it has 'cleanup 0 items' before it dies.
Have you tested on an actual player, and if so, does it work for you there?
It performs the (dummy) cleanup OK on a Clip+ 3.8, ie it returns normally to the RB UI.
The SDL-messages sort of imply that it could have something to do with the simulation, or?