[U-Boot] mmc erase fails from U-Boot command line

[Cliff Brust <cliff.brust@defengcorp.com>]

I have the need to erase our eMMC from U-Boot on our custom board due to 
a hard wired boot up configuration. Our design is based on the Freescale 
i.MX6Q SabreSD Board reference design. The bottom line is the U-Boot 
command "mmc erase" is failing with the error "Timeout waiting for DAT0 
to go high!".  Here's a list of the U-Boot commands issued and the 
result of each so you can see what is going on.
----------------------------------------
=> mmc list
FSL_SDHC: 0
FSL_SDHC: 1 (SD)
FSL_SDHC: 2 (eMMC)

=> mmc dev 2
switch to partitions #0, OK
mmc2(part 0) is current device

=> mmc info
Device: FSL_SDHC
Manufacturer ID: 45
OEM: 100
Name: SEM08
Tran Speed: 52000000
Rd Block Len: 512
MMC version 4.4.1
High Capacity: Yes
Capacity: 7.4 GiB
Bus Width: 8-bit
Erase Group Size: 512 KiB
HC WP Group Size: 16 MiB
User Capacity: 7.4 GiB WRREL
Boot Capacity: 2 MiB ENH
RPMB Capacity: 128 KiB ENH

=> mmc erase 0 0x400
MMC erase: dev # 2, block # 0, count 1024 ...
Timeout waiting for DAT0 to go high!
mmc erase failed
0 blocks erased: ERROR
----------------------------------------

Any insight on this issue is greatly appreciated.
Thanks,  Cliff