Hi,
you can't read directly an Excel file using the LV file functions like if it was a text-based file.
You have to use Excel activeX methods and property; doing a search on the Dev.Exchange you will find several examples to import excel data from a spreadsheet to LV.
Here are a couple of links:
http://sine.ni.com/apps/we/niepd_web_display.DISPLAY_EPD4?p_guid=B45EACE3F15456A4E034080020E74861&p_node=DZ53003&p_submitted=N&p_rank=&p_answer=&p_source=External
http://sine.ni.com/apps/we/niepd_web_display.DISPLAY_EPD4?p_guid=B45EACE3F15456A4E034080020E74861&p_node=DZ53003&p_submitted=N&p_rank=&p_answer=&p_source=External
Good luck,
Alberto