I bought a Seagate FreeAgent 750GB drive & attempted to erase it & received the same error.
BTW: It was SAFE to power it off & start Disk Utility again.
I found I had to partition it first, but I was able to create one large partition.
I found these instructions on Seagate's site (of course, after I figured it out):
Open Finder > Applications > Utilities > Disk Utility
Select the external drive and click on the Partition tab
Click on the Current Volume Scheme drop-down menu and divide the drive into 2 (or more) partitions ............I did not do this....I created one!!!!!
Click Options. From the Partition Schemes provided, click on the GUID Partition Table radio button. Click OK.
Click Apply. The Partition Disk screen opens.
Click Partition. At this point, the volume dismounts from the desktop and the drive is partitioned and formatted into multiple drives with GUID Partition Table scheme.
Note: When Volumes are created, Time Machine may open asking if you would like to use the volume for backups. Click Cancel to proceed.
When finished, select the Disk Utility from the Apple Menu and choose Quit Disk Utility (recommended)
Relaunch the Disk Utility, select the external drive
and click on the Partition tab
Click on the Current Volume Scheme drop-down menu and select One (1) partition.
Click Options. From the Partition Schemes provided, click on the Apple Partition Map radio button. Click OK. Select other options as desired (e.g., Volume Name, Install Mac OS 9 Drivers, etc.).
Click Apply. The Partition Disk screen opens.
Click Partition. At this point, the volume dismounts from the desktop and the drive is partitioned and formatted into multiple drives with Apple Partition Map scheme.
Note: When Volumes are created, Time Machine may open asking if you would like to use the volume for backups. Click Cancel to proceed.
When finished, select the Disk Utility from the Apple Menu and choose Quit Disk Utility (recommended)
Charlie
