Windows cannot be installed to this disk.The selected disk has an MBR partition table.On EFI systems,Windows can only be installed to GPT disks.

The MBR and GPT are ready for a Windows installation using the legacy BIOS - Hybrid MBR method. The Installer should ask you to format the current BC FAT partition to NTFS before the installer starts copying files.

This is what you should follow - https://help.apple.com/bootcamp/mac/5.0/help/#/bcmp173b3bf2.

Your 2011 Mac does not support USB booting properly. A USB installer requires modifying Bootcamp Info.plist for your specific model, which addresses creation of the USB Installer, but does not address the execution of it to boot from.

Use BCA to remove the current partition, burn the W8,1 ISO to a physical DVD. The ISO should be about 4+GB. Re-run BCA after inserting your DVD in the Optical drive and follow prompts.

The current procedure on the Apple website is for 2012 or later Macs.

This is the Bootcamp 5 link that may also help - https://help.apple.com/bootcamp/mac/5.0/help/#/bcmp173b3bf2.

Windows can't be any further back on the drive than the third partition in order to be bootable. You cannot install it on partition four.

Edit: Forgot to add. GPT means GUID Partition Table. For any computer with EFI, which includes newer PC's, not just Macs, the old Master Boot Record way of partitioning drives for Windows is gone.

The drive will need to be completely repartitioned as GUID before you can install Windows.

And you mean the flash drive i suppose?

Since your initial post reads you're trying to install Win 8.1 from a USB drive, I would presume you're installing Win 8.1 to a different drive. Whatever device Drive 0 is in your screen shots.

If you actually mean the Win 8.1 installer is on the USB drive on either partition 1, 2, or 3, and you want to install it back to the same drive on partition 4, you cannot do that at all. Windows itself does not allow the installation on any external drive.

Before going any further, is this what you're trying to do? Also please clarify. Is the installer (the .iso image) on the USB drive, and you're trying to install Windows to a separate hard drive (or SSD)?

There are two methods to install Windows on a Mac.

1. Legacy MBR method, used on preUEFI-compliant Macs (prior to Late 2013 Macs).

2. EFI only.

As a result i cannot proceed with the installation of windows 8.1 pro in my mid 2010 MacBook Pro.

This Mac only supports a Hybrid MBR method. EFI boot will cause pain and grief.

Mixing the two methods is not recommended and will cause hardware devices to malfunction, primarily GPU and Audio, wireless adapters too. If you use the Alt/Option key and choose EFI boot, there should not be an MBR on the disk. BCA normally will create a 1:1 mapping between GPT and MBR. This is a Hybrid MBR.

BCA (if the option to create a USB installer is offered), will merge BC drivers and Windows ISO to a USB2 flash drive. Do not use a USB3 flash device for such an installer. BCA will happily create one, but Windows installer cannot read it and you will get a black screen, no boot device or your keyboard/mouse will not function.

From the OSX Terminal, please post the output of the following commands. The first command shows the GPT and the second shows the MBR.

sudo gpt -vv -r show /dev/disk0

sudo fdisk /dev/disk0

You currently do not have a Bootcamp partition and your entire disk is in a protective MBR partition. Can you run BC Assistant and partition. Do not use EFI boot. If it fails, do not delete the bootcamp partition. Post the output of the same two commands.

IF your Mac has a SuperDrive that won't accept disks, and you've been told it's because someone stuck a nonstandard disc in there so many times you are actually starting to believe it, and/or you've been told by an Apple Genius in an Apple Store that your SuperDrive doesn't accept discs anymore anymore because it's "legacy" hardware, and that's why you are trying to install Windows from an external drive, THEY ARE MOST LIKELY ALL WRONG.

Before you try anything else, do this:

https://youtu.be/5b48mtDrB_s

If you do this and your SuperDrive magically accepts discs again, so you can put your real Windows installation disc in it again, then you will be one happy Boot Camp-er.

Thanks for the help with this, but I'm still having problems.

I removed my partition with BCA, burnt the W8.1 Iso (from the microsoft website) onto a physical DVD, but my BCA isn't recognising it. Im getting the 'The installer disc could not be found' error message.

Im not sure about the SL bit.

So the burning method was;

1 Mount the Windows ISO file so that it appears in the left side of Disk Utility. Highlight the Windows ISO file on the left side of the window.

2 Choose File > New Image, and then select your Windows ISO file from the submenu.

3 Choose DVD/CD master from the Image Format menu, then choose none from the Encryption menu.

4 Give the new file a name, then click Save and save it in an easy to locate location . If prompted, enter an administrator user name and password. A progress bar appears while the image file is created (it might take some time to create the image file).

Then burn the new file to a blank DVD. - Which was to drag the created file onto the disk i inserted and click burn.

Your method is unlikely to work. You may waste a DVD, but try this.

1. Unmount the ISO.

2. Right-click on the ISO file in Finder or Desktop depending on it's location, and choose Burn.

3. Expand the Burn box and and choose options as appropriate. Burn on as slow a rate as possible.

4. Check the Verify after burn and mount options.

5. Test.

This form has been the most helpful so far.

I have this same problem, with installing Windows 8.1 on a MacBook Pro Late2011.

Can anyone help me?