A bit of background first: I've recently set up a dual boot system with two copies of XP Pro - one kept clean, used mainly for games, one I can screw up as much as I want. And yes, I do actually own two copies... I was conned into buying the Win98 Upgrade... Setup: Two hard drives, each with a small OS partition at the beginning, and the rest partitioned for storage and games, all NTFS. Up until now, only the OS partitions and one of the storage partitions contained any data, and both OSs were able to access all files and folders without a problem . I just copied 10GB of files (the ones which survived this little ordeal...) from one storage drive to the other. Once it was done, a small number of files and folders wouldn't open, giving the error message "______ is not accessible. Access is denied". In fact, after this point, any file I created on this partition I was unable to access. Create a copy of a working file, and the copy will give the same error. Nothing on the drive would open under the other OS. I can, however, restore full access for one OS at a time through the security settings. But I don't understand how the access permissions ended up different from all the other drives in the first place... Anyone know what is going on here? Although I can work my way around it if it happens again, I'd much rather prevent it in the first place... The only thing I can think of is to reinstall Windows again with the same machine name, user name etc. and hope it can't tell the difference between the two... At the very least, can someone tell me how to grant access for both OSs at the same time? The security settings are intended for networks (obviously), and as I can never "see" the other OS, I don't know how to set it any permissions.