On the main dashboard of your macOS, open the Finder app and access the Utilities folder.Here’s are some quick step-by-step instructions that will walk you to the process of forcing the system to create a new partition map via Disk Utility: Creating a New Partition Map via Disk Utility Since there are 2 different ways that will allow you to do this, we’ve put together 2 different sub-guides that will walk you through the process of creating a new partition map.įell free to follow whichever one is closer to your preferred way of troubleshooting macOS issues:Ī. This is confirmed in situations where the Couldn’t modify partition map error is being caused by a system action that ends up corrupting the partition map. Now that you are aware of every scenario that might trigger the Couldn’t modify partition map error, here’s a list of methods that might allow you to fix it: Method 1: Creating a New Partition MapĪs it turns out, a lot of affected users that were also dealing with this issue on macOS have managed to fix the issue by using Disk Utility to create a new partition map by forcing the utility to show all devices and erasing the problematic partition.

If this fails, you should attempt to mont a healthy macOS state via the Time Machine utility. In this case, you should be able to fix the issue by initiating a repair disk operation via the Recovery Menu. Corrupted OS files – Under certain circumstances, you can expect to see this issue occurring in situations where you’re actually dealing with some type of system file corruption that is affecting the reformatting operation.In this case, you need to flip the Locked/Unlocked switch in order to fix the issue. SD Card uses is ‘Locked’ – Keep in mind that if you’re using an older SD card (especially from SanDisk) when encountering this issue, it’s possible that the operation fails because the external device is locked, so new info cannot be written on it.If you find yourself in this particular scenario, you should be able to fix the issue by creating a new equivalent via Disk utility or directly via the Terminal app. Missing / Corrupted Partition map – One of the most common scenarios that might cause this problem is an instance in which the required partition map is either missing or severely corrupted.

Could not unmount disk when formatting