It always helps if you post the VI job.

VI_ImportJobDefinition.pdf

I believe on the "WO" it should be "/WO"

Invoice Type might need to be above the Invoice No.

The Error is clearly on the header - see attachedVI_JobLogReport.pdf

I know, which is why I said what I did.  The order things are done does matter.

If you get Next before setting invoice type, Sage may have already assumed it was IN (open the Entry screen and try it)... making it impossible to change to CM after that.  Type and ApplyToInvoiceNo would become unavailable for input. 

The help files indicate type comes before the Next invoice number is selected.

Changing the order didn't seem to have any effect.  I tried adding some additional fields but effect is the same

6724.VI_JobLogReport.pdf

"Invalid or Write Failed column is not in the IOList."

This means you are importing to a column which is not available for writing at that time.

Are you sure that invoice # exists in history for that customer?

"Invalid or Write Failed column is not in the IOList."

This means you are importing to a column which is not available for writing at that time.

Are you sure that invoice # exists in history for that customer?

Yes, definitely there

I tried removing the Apply to Invoice No field from the import, same error

I tried assigning the CM number (instead of using the NEXT function, same error

I tried separating the header and line item, same error

Is it possible that the import is looking for something else in the invoice type besides CM?