Specifics would be nice on the computer. Also is the drive internal or external? Anyway make sure that you have it formatted properly. If the drive is formatted on an Intel machine its being defaulty formatted to GUID format scheme, so youll have to go into Disk Utility and go to partition then options and select Apple Partition Map instead of GUID. Also, it may be that the drive is not being formatted properly. Format it again with different software and try again. Also check in Disk Utility that the drive has "Owners Enabled" (bottom of disk utility). If not, then something is not going right and you will have to manual enable owners via terminal and vsdbutil