xls to xlsm conversion problem
 

When I convert a 2003 xls workbook to 2007 xlsm workbook that contains macros
and references to other workbooks I received this message

"Excel found unreadable content in 'xyz.xlsm'. Do you want to recover the
contents of this workbook? If you trust the source of the workbook, click
yes"

When I click yes it replaced all the references to other workbooks with the
actual values. Luckily I kept a copy of the original xls workbook. Any idea
how to fix or find what the unreadable content so I can successfully convert
it?