When you attempt to open a PDF in PDF2XL, you may encounter this error:

This indicates that your PDF file has somehow become corrupt and is in need of repair.

You can try opening it in Adobe Acrobat and re-saving it, or run it through a PDF repair tool. Here is a free online tool if you don't wish to purchase a toolkit:
​ http://www.pdfaid.com/repair-pdf-file.aspx