I have just had an external hard drive from an old windows/lynx box put into an enclosure as the old box has died. When connected this unit to my macbook pro the mac finds the drive and will let me access all the files. It will however not allow me to erase any files or write any new files. I think the computer shop tested the drive on a windows machine not a mac. Is there any way i can make this drive a read/write unit?