Does the layout of the workbook differ from the other files that you are trying to import?
What happens if you change the workbook spec to the following:
<workbook>
<sheet headerRow="2" />
</workbook>
Can the file be imported on it's own (i.e. specifying the filename in the node's 'File' property?
Can you create a copy of the file with just the first three rows (with the data row containing dummy data), confirm it still gives the same error and attach it to this post?