Firmware updates for Intel-based Macs require a GUID partition scheme
Firmware updates will not install on an Intel-based Mac if the computer is using a non-standard partition scheme, such as an fdisk scheme. You may see an "unexpected error occurred (0); unable to upgrade firmware" error message, or your computer may start normally (after a single beep if the power button is held) when attempting to install the firmware update.
Discovering the partition scheme
You can easily find out what partition scheme a disk has using Disk Utility.
Open Disk Utility:
If your Mac started from a Mac OS X installation disc, choose Utilities > Disk Utility.
If your Mac started from a Mac OS X volume, open Disk Utility from the Utilities folder. You can get there by choosing Go > Utilities.
Select the hard disk (not the volume) in the left side of the Disk Utility window. The disk usually contains the name of the drive vendor, not "Macintosh HD" or a name you have chosen.
Tip: In Disk Utility, volume names are indented on the left side of the window. Disk names are not indented.
Click to select the drive.
Look for the "Partition Scheme:" line at the bottom of the screen. An Intel-based Mac can only install firmware updates on a disk with the "GUID Partition Table."
Solution
If your partition scheme is not "GUID_partition_scheme," you will need to back up your data, repartition the disk, and reinstall Mac OS X.
This will erase the disk and allow you to install the firmware update. Important: Back up your important data. Partitioning a hard disk erases all data on the disk.
Back up your important data. Partitioning a hard disk erases all data on the disk.
Start from your Mac OS X installation disc, then choose Utilities > Disk Utility.
Select your computer's hard disk.
Click the Partition tab in the Disk Utility window. If the partition tab is not visible, make sure you've selected the disk (not volume) in the left side of the window. The disk usually contains the name of the drive vendor, not "Macintosh HD" or a name you have chosen.
Tip: In Disk Utility, volume names are indented on the left side of the window. Disk names are not indented.
Choose the desired number of partitions from the Volume Scheme pop-up menu. It's OK to choose "1 Partition" if you only want one.
Click Options.
Note: On some Intel-based Macs, the Options button does not appear under the partition tab. Use the erase tab to erase the disk instead. This will change the partition scheme to the default "GUID Partition Scheme." You can then use the partition tab to create additional partitions if desired.
On the Partition Scheme sheet, choose "GUID Partition Table."
Click OK.
Make any other changes you wish in the Volume Information section, such as partition size or naming.
Click the Partition button to erase and partition your disk.
When partitioning finishes, reinstall Mac OS X on the volume.
After reinstalling Mac OS X, download and install the firmware update for your computer. Afterwards, you can restore your backed-up data.