I get that sometimes on XP. Have to reboot my machine before the file locks are gone. Even though PBoost says it's Poser doing it, sometimes the operating system makes locks too. If you have Poser 5 you can point it to your Poser 4 runtime, no problem. You do it from the top level in the Poser 5 libraries panel. If you use Vicky 3, make a copy of the !Daz folder in runtime:libraries in Poser 4 to the same spot in Poser 5.