I would assume you're running a windows server from the location you have set up for your xcache dll (plus dlls are windows only). Koloxo is a control panel so doesn't tell us if you're running apache or not. However I would guess your problem is here:
xcache.mmap_path = "/tmp/xcache"
that's a linux filepath - fix it and restart whatever you use if it isn't apache and try again
If that doesn't help I would suggest going to the xcache site for support as this is certainly an xcache issue not a vbulletin/vboptimse issue