Converting from Excel 2002 to PDF with Acrobat Pro 6.0

When I try to convert a document from Excel 2002 to PDF using Acrobat Pro 6.0 most of the document turns into a black square. Some of the text comes through. but the bulk of the form shows as a large black square which appears to overlay the field of the document. I had been doing this successfully for several years with these same programs, but last week I started having this problem. It seems like something changed a setting in one of the programs. I am using Windows XP Home SP2.