iDoc extension for HRMD_A07 - Error message B1-070

I am trying to create a custom extension to HRMD_A07 to capture some additional data added to infotype 0001. I have gone through the WE31, WE30, WE82, SM30 transactions to create the extension but when I try to test with PFAL I am getting the message B1-070.

Internal error: Program read table idoc_structure, command

data_select_for_block, argument ZHR_SEG

The extractor appears to be trying to fill in the original HRMD_A07 basic type and the HRMD_A07 with the extension.

Any hints?

Thanks, Rob.