Does anyone know how to download an excel file without the attached error popping up? Is there some type of setting in NetSuite or Excel I need to update?

Just download CSV, excel generated by NS is in XML format, which may show this error. Simply download CSV file instead , format free flat file and open it using Excel

@Jackie if this is a one off situation then downloading as CSV is a good option (see screenshot). If it's something you do often you can use CloudExtend Excel to see and run your NetSuite searches directly from Excel bypassing the NetSuite UI entirely.