Kernel 2.6.17 and RAID5 Grow Problem (critical section backup)

[Justin Piszcz <jpiszcz@lucidpixels.com>]

p34:~# mdadm /dev/md3 -a /dev/hde1
mdadm: added /dev/hde1

p34:~# mdadm -D /dev/md3
/dev/md3:
         Version : 00.90.03
   Creation Time : Fri Jun 30 09:17:12 2006
      Raid Level : raid5
      Array Size : 1953543680 (1863.04 GiB 2000.43 GB)
     Device Size : 390708736 (372.61 GiB 400.09 GB)
    Raid Devices : 6
   Total Devices : 7
Preferred Minor : 3
     Persistence : Superblock is persistent

     Update Time : Fri Jul  7 08:25:44 2006
           State : clean
  Active Devices : 6
Working Devices : 7
  Failed Devices : 0
   Spare Devices : 1

          Layout : left-symmetric
      Chunk Size : 512K

            UUID : e76e403c:7811eb65:73be2f3b:0c2fc2ce
          Events : 0.232940

     Number   Major   Minor   RaidDevice State
        0      22        1        0      active sync   /dev/hdc1
        1      56        1        1      active sync   /dev/hdi1
        2       3        1        2      active sync   /dev/hda1
        3       8       49        3      active sync   /dev/sdd1
        4      88        1        4      active sync   /dev/hdm1
        5       8       33        5      active sync   /dev/sdc1

        6      33        1        -      spare   /dev/hde1
p34:~# mdadm --grow /dev/md3 --raid-disks=7
mdadm: Need to backup 15360K of critical section..
mdadm: Cannot set device size/shape for /dev/md3: No space left on device
p34:~# mdadm --grow /dev/md3 --bitmap=internal --raid-disks=7
mdadm: can change at most one of size, raiddisks, bitmap, and layout
p34:~# umount /dev/md3
p34:~# mdadm --grow /dev/md3 --raid-disks=7
mdadm: Need to backup 15360K of critical section..
mdadm: Cannot set device size/shape for /dev/md3: No space left on device
p34:~#

The disk only has about 350GB of 1.8TB used, any idea why I get this 
error?

I searched google but could not find anything on this issue when trying to 
grow the array?