Xlsm file odd security setting when created in Excel 2003

I have an Excel macro which converts a .prn text file to a .xlsm macro-enabled spreadsheet.  On a Windows 7 Home Premium machine with the Office Compability Pack installed, running Excel 2003, the spreadsheet created has an odd security setting: in the Security tab of Properties for the file (viewed in Windows Explorer/My Computer), the group "Everyone" is missing. The result is that I cannot view the file when I connect from another, networked computer. I have other macros which convert .prn files to .xls spreadsheets, and they do show the Everyone group, with Full Control permission enabled.

Checking a bit more, I get the same behavior (no Everyone group) if I open a .xls spreadsheet and save it as either .xlsx or .xlsm. I also notice that the icon in the folder listing is slightly different; there's a gold padlock superimposed on the Excel icon. The padlock disappears if I create the Everyone group in the Security tab and give it Full Control.

I don't have this problem when I run the macro in Excel 2007 on another Windows 7 computer, but I have no way to verify whether it's something unusual in one of the computers, or a difference between Excel 2003 and 2007.

I can't see anything in the Excel options tabs that would seem to relate to this, though I may just not be looking in the right place. Any ideas on how to make these worksheets automatically visible & enabled to all in the Everyone group?