"a file called world.xx might be currupt is says ffs"
The install program give an error message? You can try manually extracting that file, re-install the patch (if you have not done that yet), then delete the corrupt world.x1 file from a save before you defeated the succubus, and re-load (the game will replace the missing file with the default version).
See
Troubleshooting Tips (& manual install procedure) 
