What does this error mean in idoc_apapter

Hi,

Im getting this error while doing a flat file to an idoc scenario.

<SAP:Code area="IDOC_ADAPTER">ATTRIBUTE_WRONG_INTF</SAP:Code>

<SAP:Stack>Unable to interpret IDoc interface MI_ZPURCHASEORDER01_Inb</SAP:Stack>

Can anyone explain me what to do.

Thanks in advance,

Bhargav