Cannot Open 2007 file in 2003

I have a file (.xlsm format) that was created in Excel 2007.  When it is shared with 2003 users, they cannot open it.  The 2003 users do have the Compatabilty pack installed.  Is something else needed to open the .xlsm format?

Chris

Here is the knowledge base article on the Compatibility Pack

http://support.microsoft.com/kb/924074#Issues

As you can see, in 2003 all formats ca be read from 2007. I would wonder if however all your 2003 installations are fully patched to SP3?

Microsoft offers a file conversion utility. Some functionality gets compromised and you get serious warnings coming at you regarding that 2007 has more rows, blah blah blah.