Windows – ExFAT partition on External HDD not showing up on Bootcamp Windows 7

To share with other users facing a similar situation, here is how I solved the problem--and avoided completely reinstalling OS X and Windows. For reference, my OS X version was Mountain Lion when I started solving the problem--and I needed to upgrade to Mavericks in the end.

1. Back up Windows partition with WinClone to an external HDD
2. Run "Backup now" in Time Machine to make sure I have a latest backup of OS X partition
3. Under OS X Disk Utility, remove Windows system partition (which is typically labeled BOOTCAMP)
4. In OS X Recovery boot, remove OS X partition and create it from the scratch (make it use whole HDD space)
5. Install a clean OS X (my MBA 2011 allowed only Lion--if I remember correctly, it's fine as long as it's not a later release than my Time Machine backup)
6. Restore my OS X partition from Time Machine. It makes Recovery Partition disappear, we'll fix it in the next step
7. From AppStore, reinstall Mountain Lion. It's only needed to re-create the Recovery Partition.
8. Under OS X Disk Utility, manually create a FAT partition for Bootcamp following WinClone support article. WinClone will convert it into NTFS in the next step.
   This is where you decide how HDD space will be split between OS X and Windows.
9. Restore Bootcamp partition from your backup (#1) to the Windows partition you created in #8.
10. Boot Windows under Bootcamp; it can run CHKDSK automatically, reporting that volume could be dirty--but didn't find any problems.
11. If you use Trackpad++, it needs to be reinstalled now. Boot Windows under Bootcamp, reinstall PowerPlan Assistant first, then Trackpad++.
12. Under OS X, re-create virtual machine in Parallels.
13. Upgrade to Mavericks.
14. Move to Bootcamp system partition all the data files that were originally stored on Windows data partition (provided you have their backup).

The only problem that's left at this point is that Parallels freezes VM when used in "all apps in one window" default mode (which is not Coherence, Fullscreen or Modality mode). Will seek solution for it later; at least it is stable for a week now in Coherence mode.

Before following the above sequence, I tried to recreate data partitition with Windows, converting the unallocated space that sized exactly like the lost partition. Failed: I found that there is a new partition which originally wasn't there: sized 620MB, but it didn't appear as recovery partition among Startup Disks on boot. Didn't try deleting it though, maybe it could help.

I was able to install Windows after doing two things. I'm not positive which one did the trick as I did them both in between an attempt to run bootcamp. These are the things I did in order:

1. Install reFind... doing this added the missing EFI partition that was mentioned I was missing in the comments for this question.
2. Use the reFind partition editor to fix the Master Boot Record (MBR) table for my HDD. This partition editor can be found on the reFit menu (launched by choosing the reFit option on the reFind menu)

After this, I launched mac, started boot camp, and the 'status: partitioning disk' message/bar restarted and then it was able to finish partitioning and I have since installed Windows successfully. Any hints on why this finally worked would be much appreciated!

Also, something to note is that after I installed reFind, my partition table (output to diskutil list) was:

/dev/disk0 (internal, physical):
#:                       TYPE NAME                    SIZE       IDENTIFIER
0:      GUID_partition_scheme                        *500.3 GB   disk0
1:                        EFI EFI                     209.7 MB   disk0s1
2:                  Apple_HFS MAC HDD                 500.1 GB   disk0s2