OpenXML Excel program error

Question

I am getting the following error when I try to open the file.  I just started testing this and I do not know what to do.  So the code is very preliminary.  The code for the class is attached.  I only have about a year of C# experience and have not used OpenXML before and the lead programmer is hard to work for.

I want to be able to send a table (or change it to a list or class or something) to this class to make a xlsx spreadsheet.  We want to eliminate the need for Excel.  This is for health care field. 

Thanks for any help I can get on this.

Arep

Replaced Part: /xl/worksheets/sheet.xml part with XML error.  A document must contain exactly one root element. Line 1, column 0.