Thanks Thomas... Yep it's a real mystery. I have personal experience of this as I started writing PBooost on win98. I then upgraded to XP Pro and had no problems. I then converted to NTFS to re-create Rons problems (he was testing also... on XP home NTFS) and found occasional lock-ups. I totally FDisked and re-formatted and installed Win 98 then upgraded again to XP, again with FAT 32... Totally clean installations. Now PBooost FAILS while Poser is running! Odd in the extreme... I've tried just about every XP tweak to stop the problem to no avail. I have no network. Maybe I took the easy route out, or maybe I had a sudden flash of "intelligence" by creating the tester app., I don't know. As long as everyone knows where they stand with PBooost. At the moment... until I have more hair-frazzling inspiration... it's the best I can do! But I'm still researching the more scary parts of NT/XP file system...! Howard:)