We talkling Mac or PC? If mac, ss the suspect Mac running OS 10.4.11? I was recently reformatting a production Mac and re-installing the major apps (CS2, CS3, QuarkXPress, etc.). Before installing any apps, I performed all Mac OS X 10.4 updates all the way to 10.4.11.

I installed QuarkXPress 6.1 and it was fine. When attempting to update to 6.5 I would get the same error as you described. I tried Repairing Permissions, FSCK, all the tricks I know and tried running the update several more times—no luck.

I resorted to reformatting the drive again, but this time, I left it at 10.4.7. Then I did the whole QuarkXPress install again and updated to 6.5. No problems. Went all the way to 6.52, all was OK. I then proceeded to update to OS X 10.4.11. All was still golden.

Hence, I think there is a conflict between the Quark 6.5 installer and Mac OS 10.4.11.