Rather than repeat it, let me refer you to another, related thread. You may have a drive formatted with a non-Apple driver, which Installer will not wish to deal with. You will need to replace the driver (not the formatting) with an Apple driver, or use the option not to update Apple drivers from the Installer, or use the same disk utility to reinstall the driver, and still use the option not to update the (non-Apple) driver from within Installer.

'Non-Apple driver' may include non-Apple formatting. However, in that case, the system is likely to quack that it cannot read the drive at all, and do you wish to erase it (a slipshod expression of inviting you to reformat from PC to Apple format).

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