The unattend answer file contains an invalid product key

Hello:

I am using MDT 2010 trying to deploy Windows 7 Enterprise 64-bit.  We have our KMS server up and running just for a little background.  I keep getting the error during the build process:

The unattend answer file contains an invalid product key.  Either remove the invalid key or provide a valid product key in the unattend answer file to proceed with windows installation.

I tried the following:

opened up my deployment work bench
- choose the task sequence with the required WIM
- Selected Edit Unattend xml
- Expanded Components
               - 1 windowsPE
               - amd64_micrsoft-Winows-Setup_netural
               - User Data
                 -Product Key

- Then Right Clicked on the Key string and choose  "Write Empty String"

Thanks for the help.