Syncing Excel prevents changing spreadsheet

I have created a spreadsheet in XP Pro using Excel 2007. I placed it in my
ActiveSync folder to be synchronized to my smartphone using ActiveSync 4.5.
When it is copied to my smartphone I open it with Excel Mobile 6.1, and get
the message "This document is protected or marked read-only. You will not be
able to edit this document." I have repeatedly marked the spreadsheet
unprotected (in Windows), and have unlocked all cells. There are two
worksheets in the workbook, and I have done this to both worksheets. I have
repeatedly synced the unprotected workbook, and have shut off and rebooted
my phone.

I cannot find any menu items in Excel about marking it read-only, but when I
select Properties in Windows Explorer it says it is not read-only.

How do I make my spreadsheet usable on my phone?

Thanks,
Iam