heh. has same issue. THANKS for INFO!!
though I didn't need to disable it. just FLASH the CACHE (which is a feature of vbOptimise)
Note: "ladders and tournament" add-on makes a similiar error and new prefix sets show up blank when you create NEW ones in the vb admincp.
To solve: disable add-on, then make new prefix, turn ladders and touranment add-on back on (enable). All good.